1.1) How secure is Solaris 2?
Solaris 2 is relatively secure, considering that it is a general-purpose, time-sharing, multi-user operating system. Such systems are inherently full of compromises. Solaris 2 is a version of Unix which was not designed for security. However, Sun actively fixes security holes. Additionally, there are facilities that can increase the security of Solaris (see section 3).
Specifically, Solaris has been designed to meet the TCSEC (Orange Book C2) level for security. According to Sun, Solaris 2.4SE is ITSEC E2/F-C2-certified. Solaris 2.6 is currently undergoing both the ITSEC E3/F-C2 and TCSEC C2 certification processes. Current information can be found at http://www.sun.com/solaris/2.6/ds-security.html.
In order to build a system that actually meets the evaluation there are a number of patches that must be installed. A bundle of the exact patches used for the evaluation can be obtained directly from Sun.
For those that need more security than provided by C2 Sun provides a version of Solaris that meets was designed to meet the TCSEC CMW (Compartmented Mode Workstation) level, which exceeds B1.
Trusted Solaris 1.2 F-B1/E3 (Based on SunOS 4.1.3_U1) Trusted Solaris 2.5.1 F-B1/E3 (Based on Solaris 2.5.1 11/97)
1.2) What version of Solaris should I run?
Where security is concerned? Each subsequent release of Solaris has been an improvement over its predecessor. Solaris 2.7 is currently the latest release, and also the most secure.
1.3) Can I just install a machine and ignore it?
Most installed machines suffer from entropy: They lack a current OS release, and up-to-date patches and tools. It's important to install the latest patches, at the least, to be sure that all known security holes are filled.
1.4) What is the single most important step I can take to secure a Solaris machine?
Keep the security patches up-to-date. According to CERT, many systems are compromised by exploiting known bugs for which patches exist. Simply keeping patches up-to-date, especially on "exposed" machines, will greatly decrease the chance of a break-in.
2) How can I configure Solaris to make it more secure?
2.1) What file permissions should I change?
The program
fix-modes runs on Solaris 2.4 and 2.5 and changes system file and directory permissions. The new permissions make it harder for non-root users to become root, and for non-root users to modify system files.2.2) How should I change root user configuration?
Be sure root has a
umask setting of 077 or 027.Be sure root has a safe search path, as in/usr/bin:/sbin:/usr/sbin
2.3) How should I change startup files?
Generally, examine all "S" files in /etc/rc2.d and/etc/rc3.d. Any files that start unneeded facilities should be renamed (be sure the new names don't start with "S"). Test all boot files changes by rebooting, examining/var/adm/messages, and checking for extraneous processes in
ps -elf output.2.4) How can I disable network root logins?
Make sure the to enable the "CONSOLE" line in/etc/default/login. To disable use of ftp by root, add "root" to /etc/ftpusers.
2.5) How do I disable
rlogin/rsh access?Remove /etc/hosts.equiv, /.rhosts, and all of the "r" commands from /etc/inetd.conf Do a
kill -HUP of theinetd process.2.6) What accounts are unnecessary?
Remove, lock, or comment out unnecessary accounts, including "sys", "uucp", "nuucp", and "listen". The cleanest way to shut them down is to put "*LK*" in the password field of the /etc/shadow file. Also consider using the
noshell program to log attempts to use secured accounts.2.7) How to I protect devices?
The file /etc/logindevperm contains configuration information to tell the system the permissions to set on devices associated with login (console, keyboard, etc). Check the values in this file and modify them to give different permissions.
For removable media the BSM subsystem provides the allocate and deallocate commands that ensure that only a single user can access removable media (such as tapes) at any one time.
2.8) What permissions should I change in /etc?
No file in /etc needs to be group writeable. Remove group write permission via the command
chmod -R g-w /etc2.9) Why do Solaris machines act as routers?
By default, if a Solaris machine has more than one network interface, Solaris will route packets between the multiple interfaces. This behavior is controlled by/etc/init.d/inetinit. To turn of routing on a Solaris 2.4 (or lesser) machine, add
ndd -set /dev/ip ip_forwarding 0 at the end of /etc/init.d/inetinit. For Solaris 2.5, simplytouch /etc/notrouter. Be aware that there is a small window of vulnerability during startup when the machine may route, before the routing is turned off.2.10) How do I disable automounter?
Automounter is controlled by the /etc/auto_*configuration files. To disable automounter, remove those files, and/or disable the /etc/rc2.d/S74autofs.
2.11) How to I disable NFS service?
NFS exports are controlled by the /etc/dfs/dfstab file. Remove this file. To disable the NFS server daemon, rename /etc/rc3.d/S15nfs.server. To prevent a machine from being an NFS client, rename/etc/rc2.d/S73nfs.client. When renaming startup files, be sure to name them with a starting letter other than "S".
2.12) Do I need to worry about
cron jobs?Review all the
cron jobs by reading the cron file of every system account in /var/spool/cron/crontabs. Consider logging all cron activities by setting "CRONLOG=yes" in/etc/default/cron.2.13) Are there any risks to using dynamic routes?
Machines using a dynamic route-receiving daemon like
in.routed and in.rdisc are vulnerable to receiving incorrect routes. These routes can disable some or all connectivity to other networks. When possible, use static routes (routes added via the route commands in startup files, rather than the routing daemons.2.14) When and how should I use static ARP?
ARP is the protocol used to associate IP and Ethernet addresses. Machines that share a wire (and have no routers between them) know each others ARP addresses. If one machine is replaced with another, the ARP addresses are usually different. By default, Solaris machines dynamically determine ARP addresses. The
arpcommand can be used to statically set ARP table entries and flush all other entries. This facility is best used when there are few, unchanging systems on a network and the machines need to be assured of each other's identities.2.15) Is it unsecure to run
rpcbind?rpcbind is the program that allows rpc callers and rpc service provides to find each other. Unfortunately, standard rpc is unsecure. It uses "AUTH_UNIX" authentication, which means it depends on the remote system's IP address and the remote user's UID for identification. Both of these forms of identification can be easily forged or changed. General-purpose systems usually need rpc running to keep users happy. Special purpose systems (web servers, ftp servers, mail servers, etc) can usually have rpc disabled. Be sure to test all the facilities that you depend on to be sure they aren't affected if you turn off rpc. To disable rpc, rename/etc/rc2.d/S71RPC.2.16) What permission bits should be set on/etc/utmp?
/etc/utmp can be set to mode 644 without disrupting any service.
2.17) What programs can be un-suid'ed?
Many of the setuid and setgid programs on Solaris are used only by root, or by the user or group-id to which they are set. They can have setuid and setgid removed without diminishing user's abilities to get their work done. Consider each of these programs individually as to their use on your system. This is an example list of setuid programs taken from a Solaris 2.6 system:
# find / -perm -4000 -print /usr/lib/lp/bin/netpr /usr/lib/fs/ufs/quota /usr/lib/fs/ufs/ufsdump /usr/lib/fs/ufs/ufsrestore /usr/lib/fs/vxfs/vxdump /usr/lib/fs/vxfs/vxquota /usr/lib/fs/vxfs/vxrestore /usr/lib/exrecover /usr/lib/pt_chmod /usr/lib/sendmail /usr/lib/utmp_update /usr/lib/acct/accton /usr/lib/uucp/remote.unknown /usr/lib/uucp/uucico /usr/lib/uucp/uusched /usr/lib/uucp/uuxqt /usr/lib/sendmail.orig /usr/openwin/lib/mkcookie /usr/openwin/bin/xlock /usr/openwin/bin/ff.core /usr/openwin/bin/kcms_configure /usr/openwin/bin/kcms_calibrate /usr/openwin/bin/sys-suspend /usr/dt/bin/dtaction /usr/dt/bin/dtappgather /usr/dt/bin/sdtcm_convert /usr/dt/bin/dtprintinfo /usr/dt/bin/dtsession /usr/bin/at /usr/bin/atq /usr/bin/atrm /usr/bin/crontab /usr/bin/eject /usr/bin/fdformat /usr/bin/login /usr/bin/newgrp /usr/bin/passwd /usr/bin/ps /usr/bin/rcp /usr/bin/rdist /usr/bin/rlogin /usr/bin/rsh /usr/bin/su /usr/bin/tip /usr/bin/uptime /usr/bin/w /usr/bin/yppasswd /usr/bin/admintool /usr/bin/ct /usr/bin/cu /usr/bin/uucp /usr/bin/uuglist /usr/bin/uuname /usr/bin/uustat /usr/bin/uux /usr/bin/chkey /usr/bin/nispasswd /usr/bin/cancel /usr/bin/lp /usr/bin/lpset in/lpstat /usr/bin/volcheck /usr/bin/volrmmount /usr/bin/pppconn /usr/bin/pppdisc /usr/bin/ppptool /usr/sbin/allocate /usr/sbin/mkdevalloc /usr/sbin/mkdevmaps /usr/sbin/ping /usr/sbin/sacadm /usr/sbin/whodo /usr/sbin/deallocate /usr/sbin/list_devices /usr/sbin/m64config /usr/sbin/lpmove /usr/sbin/pmconfig /usr/sbin/static/rcp /usr/sbin/vxprint /usr/sbin/vxmkcdev /usr/ucb/ps /usr/vmsys/bin/chkperm /etc/lp/alerts/printer
Create a master list of the remaining setuid/setgid programs on your system and check that the list remains static over time.
2.18) What system facilities can I disable?
Every network on the system should be inspected to determine if the facility that it provides is appropriate for your environment. If not, disable the facility. Some of these facilities are in the system startup files, as discussed in section 2. Other are started in/etc/inetd.conf. Comment out the unneeded facilities and
kill -HUP the inetd daemon. Some common facilities are:tftp systat rexd ypupdated netstat rstatd rusersd sprayd walld exec comsat rquotad name uucp
For a very secure system, replace the standard
inetd.conf with one that just includes telnet and ftp(if you need those facilities).2.19) Should I run
in.fingerd?in.fingerd has had some security problems in the past. If you want to provide the finger facility, run it as "nobody", not as "root".2.20) Can
syslog be made to be more effective?By default,
syslog provides minimal system logging. Modify the /etc/syslog.conf file to have syslog log more information, and separate to where the information is logged by importance. Anything related to security should be sent to a file that gets encrypted. Unfortunately,syslog must be restarted for it to read the new configuration file.More login logging can be enabled by creating the "loginlog" file:
touch /var/adm/loginlog chmod 600 /var/adm/loginlog chgrp sys /var/adm/loginlog
2.21) How can the EEPROM make a system more secure?
Set the EEPROM to "security=command" password-protect all EEPROM commands except "boot" and continue". Set the EEPROM's password so no one else can change its modes. Unfortunately, this doesn't truly secure the machine. If someone has physical access to the machine, they can open the machine and replace its EEPROM. Replacing the machine's EEPROM also changes its
hostid. Recording all the hostids of your machines and checking this list against the machines occasionally to verify that no EEPROMs have been replaced.2.22) Is my machine being "promiscuous"?
Under Solaris, there is no way to determine if a machine's network interfaces are in "promiscuous" mode. Promiscuous mode allows the machine to see all network packets, rather than just those packets destined for the machine. This allows the machine to snoop the network and monitor all traffic. An interface should only be in promiscuous mode if the
snoop program, or another network monitor program, is being run. If you aren't running such a program, and your machine's interface is in promiscuous mode, then it's likely that a hacker is monitoring your network. The public domain ifstatuscommand returns a machine's promiscuous state. It is currently only ported to Solaris 2.6 and below. (See section 3.)2.23) If I need to use NFS, how can I make it more secure ?
- Any filesystems listed in /etc/dfs/dfstab will be exported to the world, by default. Include a list of nfs clients (or a netgroup) with the "-o rw" or "-o ro" options.
- Include the "nosuid" option to disable setuid programs on that mount where applicable
- Don't run nfs mount through
rpcbind- themountdaemon will see the request as being local and allow it. This is the source of knownrpcbindvulnerabilities as reported by CERT (section 4). Use therpcbindreplacement (section 3) that disables request forwarding, or be sure have installed the latest Sunrpcbindpatches which also disable forwarding. - Use secure-RPC if possible. If not, you're using "AUTH_UNIX" authentication, which simply depends on the IP address of the client for identification. Any machine using the IP address of the ones in your access list can gain access to NFS.
- Disable NFS if possible. NFS traffic flows in clear-text (even when using "AUTH_DES" or "AUTH_KERB" for authentication) so any files transported via NFS are susceptible to snooping.
- Programs can guess the file handle of the root mount point and get any file from an NFS server, regardless of any access rights. Use
fsirandto randomize inode numbers on NFS servers.
2.24)
How can I secure
sendmailWith each new Solaris release, Sun ships sendmail code updated with the latest fixes. Still, there are new bugs reported monthly. How can
sendmail be made more secure?- Consider running the latest version Berkeley
sendmail(see section 3) - Consider using
smrshor other sendmail replacements (section 3) - Remove "decode" from /etc/aliases
- Set /etc/aliases permissions to 644
- Consider using a proxy-based firewall with SMTP filtering to screen out unnecessary SMTP commands.
- If the machine needs to receive email (and thus needs an SMTP daemon running, consider a separate partition for
/var/mailto prevent spam attacks from filling/varand disabling logging et al.
2.25)
Is NIS secure, and how can it be made more secure?
NIS is not a secure distributed name service. NIS+ is more secure when configured properly. NIS will give away all the information in its tables if its domain name is guessable. To close this hole, put trusted host/net addresses to /var/yp/securenets. Also consider using secure RPC or NIS+. Finally, don't include root and other system account information in NIS tables.
2.26)
What is needed for secure anonymous ftp service?
Solaris 2.5
ftpd(1M) contains a good set of configuration directions, with the following exceptions:cp /etc/nsswitch.conf ~ftp/etc- Make sure that the filesystem containing ~ftp is not mounted with the "nosuid" option
- No files under ~ftp should be owned by "ftp"
- More detailed instructions can be found the anonymous ftp directions (section 4).
2.27) How can X be made more secure?
- Use the SUN-DES-1 option to use Secure RPC to pass X authentication/authorization information.
- Use
xhost +user@hostwhen granting access
2.28) How do I turn on SUN-DES-1 authentication?
- set
DisplayManager*authorize: true - set
DisplayManager._0.authName: SUN-DES-1 rm ~/.Xauthority- add access permission for local host via
xauth local/unix:0 SUN-DES-1 unix.local@nisdomainandxauth local:0 SUN-DES-1 unix.local@nisdomain - Start X via
xinit -- -auth ~/.Xauthority - Add yourself and remove all others via
xhost +user@ +unix.local@nisdomain -local -localhost
Now, to give user "foo" permission to access host "node":
- Give "foo" permission on "node" via
xhost +foo@ - Create appropriate xauthority for "foo" via
xauth add node:0 SUN-DES-1 unix.node@nisdomain - "foo" can now connect to "node":
xload -display node:0
2.29) What patches should I install?
Use
showrev -p to list patches installed on the system. Check Sun's patch list (section 4) for current security-related patches for the version you are running. Download and install all pertinent security patches. Recheck the patch list frequently. Not all security patches need be installed on every machine. But protect machines, or those with public access, should be kept up-to-date. The patchdiag program that is available on the SunSolve CD and at the SunSolve web site will automatically compare the patch level of a host against the current Sun recommended patch set, and display any differences.2.30) How can I prevent code from executing in the stack?
There are a whole category of security holes that depend on one system flaw: the ability to execute code from the stack. These bugs overflow a buffer such that it writes into stack space. In that space they put code that they can then execute. In this way, the bug can execute arbitrary code on the target system.
To secure your system against stack based buffer overflows, you can add the following to
/etc/system:set noexec_user_stack=1 set noexec_user_stack_log =1
The first line will prevent execution on a stack. Care must be taken though, because there are some programs which legitimately try to run code off the stack. Those programs will crash if you implement this option. Generally, if the system is single purpose and needs to be secure (i.e. a web server), you should use this option. The second line adds logging when someone does try to run an exploit.
2.31) How can I change the greeting banners?
The banner displayed during a terminal or console login comes from
/etc/motd. The default telnet banner can be changed by creating /etc/default/telnetd and adding the "BANNER" variable, as in: BANNER="\n\nThis is a secured system. Unauthorized access prohibited. All activity is logged.\n\n" The default ftp banner can be changed via a similar line in /etc/default/ftpd.2.32) How can I prevent TCP sequence prediction attacks?
In
/etc/default/inetinit, modify the variable setting "TCP_STRONG_ISS=2".3) What programs should I replace or add?
3.1)
inetd?inetd can be replaced withftp://qiclab.scn.rain.com/pub/security/xinetd*to add logging facilities. (This program apparently has not been ported to Solaris.)3.2)
ifstatus?ifstatus can determine if your network interfaces are in promiscuous mode. This program needs to grok the kernel, and has only been updated through Solaris 2.6. Until the author gets access to Solaris 7 and 8 source, or until Sun provides an interface into the kernel for this information, it will not work on those releases.3.3)
xntp?xntp is a more secure version of ntp, the network time protocol.As from Solaris 2.6, Sun ships
xntpd with the operating system.3.4)
sendmail?The most recent (and usually most secure) version of
sendmail is always available from Berkeley. Included in the sendmail package is smrsh, the "sendmail restricted shell" which can be used to control any programs invoked by sendmail.Warning: there are Sun specific modifcations that will be lost if you move to a plain Berkley
sendmail. Also, Sunsendmail patches have a tendency to replace Berkeleysendmail with Sun's sendmail. After installing patches, check that the sendmail version that you want to run is still in place.Sun is now shipping
sendmail 8.9.1b with Solaris 7.There are numerous replacements for sendmail, most designed with security involved. One of the best is <>.
3.5)
rpcbind?A more secure
rpcbind can be used to replace the standard rpcbind on Solaris machines. This version includes tcpwrapper-like functionality and disables forwarding of NFS requests through rpcbind. Sun's latest patches to rpcbind also solve this problem.3.6) Password checking programs?
Unfortunately,
passwd+ and npasswd are not yet released on Solaris. They are replacements for passwd that disallow "stupid" passwords from being used on Unix systems.A program similar to
npasswd but for NIS only is available: ftp://autoinst.acs.uci.edu/pub/uci-yppasswd According to the author (Dan Stromberg), the code for checking for bad passwords is small, and would be easy to copy into other programs.From Solaris 2.6 onwards it is possible to augment or replace the authentication mechanism used by Solaris using the PAM facility.
It is easy to implement a PAM module to ensure that users do not use dictionary words, or to implement your other local rules.
Using PAM there is no need to replace any components of the OS including passwd,login etc.
3.7)
crack?The
crack program can be used to break "guessable" passwords in your /etc/shadow file. It uses a lot of compute cycles, but will generally tell you the passwords of 10% of your accounts the first time it is run.3.8)
ftp?wu-ftp is a replacement for the standard ftpd daemon. It provides extensive logging and access control.Another alternative is the ftp daemon from openBSD. "The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system. Our efforts emphasize portability, standardization, correctness, proactive security and integrated cryptography." It's worth checking out the code and tools that they have produced.
3.9)
fix_modes?fix-modes is a shell script that makes extensive changes to the file and directory permissions on standard Solaris machines.3.10)
noshell?noshell is a program that can be used as the shell on accounts that are never supposed to be logged into. It logs the event (and prevents the login). (This program apparently has not been ported to Solaris.)3.11)
bind?The standard
bind on Solaris has known security problems (See CERT in section 4). This problems are patched over time, but the Solaris bind is generally behind the curve on patches. The current standard bind release is always available at ISC.3.12)
netcat?NetCat is a tool that is useful for security managers and crackers alike. It is a flexible network connection creator, allowing for probes of arbitrary ports between arbitrary systems.
4) What other useful resources should I know about?
4.1) Sun mailing-list?
Sun provides a security bulletin service via an email list to subscribe send email to "security-alert@sun.com" with a subject of "subscribe CWS your-mail-address". Old bulletins are available at ftp://ftp.uu.net/systems/sun/sun-dist. Phone: (415) 688-9081
4.2) Sun patches?
Sun security patches are available in two locations: http://sunsolve1.sun.com (for people with Sun contracts) ftp:// ftp.uu.net/systems/sun/sun-dist (for people without Sun contracts) Or for an http interface use http://sunsolve.Sun.COM/pub-cgi/patchpage.pl
4.3) Other Solaris FAQs?
The excellent Solaris FAQ: http://www.wins.uva.nl/pub/solaris/solaris2/
4.4) Useful newsgroups?
All of the USENET newsgroups with "sun" in their name :-)
comp.security.announce
4.5) Useful mailing-lists?
Sun maintains a "patch club" mailing list that includes details of Sun patch releases. Summaries are mailed weekly. The list also receives "EarlyNotifier Alerts" that contain important patch information. To change, add, or delete your email address to the list send mail to: SunSolve-EarlyNotifier@Sun.COM
If you want to be on one security mailing list, consider the best-of-security mailing list. Send subscription requests to best-of-security-request@suburbia.net, or for a digest form to best-of-security-d-request@suburbia.net.
Many security problems are due to bugs in the operating system or applications. To keep up-to-date on bug happenings, subscribe to the Bugtraq mailing list. Bugtraq is a full-disclosure UNIX security mailing list, started by Scott Chasin . To subscribe to bugtraq, send mail to listserv@netspace.org containing the message body "subscribe bugtraq". An archive of the mailing list is available at http://www.geek-girl.com/bugtraq/index.html.
The Florida SunFlash is a "closed" mailing list for Sun owners. It contains mostly press releases from Sun and third-party vendors. To find out about a mail point in your area, or for other information send mail to infosunflash@Sun.COM Subscription requests should be sent to sunflash-request@Sun.COM Archives are on solar.nova.edu, ftp.uu.net, sunsite.unc.edu, src.doc.ic.ac.uk and ftp.adelaide.edu.au
The Sun Managers list is an unmoderated mailing list for emergency-only requests. Subscribe and listen for a while, and read the regularly-posted Policy statement BEFORE sending mail to it. Write to sun-managers@sunmanagers.ececs.uc.edu
The "Sneakers" mailing list is for discussion of LEGAL evaluations and experiments in testing various Internet "firewalls" and other TCP/IP network security products.
You can join CIAC's mailing lists by filling out a form at the CIAC Web site.
The firewall mailing list is obviously for discussion of firewall-related issues.
5) How do I make my Solaris web server more secure?
There are several steps to installing a "secure" Web server. But what is meant by "secure"? Any machine that is publically accessible is necessarily unsecure. By putting it directly on the Internet you've already opened the front door and allowed anyone to come in and have a look. It is possible to guard the door and be sure the visitors hang out in only one room though. By installing the operating system carefully, adding tools, and adding monitoring software, your Web server can be much safer than one that uses a default installation.
A previous version of this information was published as a two-part column by Peter Galvin and Hal Pomeranz in SunWorld, April 1996 and SunWorld, May 1996
How secure does a web server have to be? The answer is, "very secure." There have been several embarrassing incidents of graffitti on very public web sites, and worse. Any number of toolkits exist that allow total amateurs to become holy terrors. The good news is that if you can beat the popular intrusion toolkits, 90 percent of the bad guys will go bother somebody else who's less secure.
While the following techniques can make a Solaris-based system very secure, they have to be combined with a strong network architecture utilizing firewalls or filtering routers (there's no point in controlling access by IP address if crackers can send you packets with spoofed addresses). Such a strong architecture can only truly exist when combined with a comprehensive security policy covering your entire organization.
Furthermore, no system is ever perfectly secure. The extra services (Web servers and anonymous FTP) that you run on the machine will always impact the overall security of the system. Don't be tempted to install other software not listed in these instructions. This machine is supposed to be secure, not convenient to administer.
5.0) Web server security checklist
Use this checklist to be sure your server is installed as securely as possible. Feel free to add to the checklist for site-specific steps, or to share your additions with us if they are general-purpose.
Check out Jean Chouanard's tool, solins. It automates a lot of the steps that are described in this checklist.
- Keep the system disconnected from the network until all is ready.
- Install just the core operating system, adding only necessary packages.
- Install recommended and security patches.
- Strip down the OS by removing startup files (carefully!).
- Disable IP forwarding in /etc/init.d/inetinit.
- Add a script to system startup to fix /tmppermissions (except on Solaris 2.5) and mount it "nosuid".
- Verify that few processes are running via
ps. - Invoke
sendmailfrom cron to process queued mail occasionally. - Install and configure
tcp_wrappers, S/Key, wu-ftp,andtripwireas appropriate to your environment. - Remove all but
wu-ftpandtelnetfrom/etc/inetd.conf, and edit /etc/hosts.allow to limit the machines that can use these daemons. - Enable logging of all telnet access to the system via
syslog. - Mount filesystems read-only and no-suid as appropriate.
- Make /noshell the default shell for all accounts except root and access.
- Remove /etc/auto_*, /etc/dfs/dfstab, p/var/spool/cron/crontabs/* (except
root). - Use static routing.
- Test your system thoroughly, including allowed access and denied access, and event logging.
- Consider replacing
sendmail, syslog, bind,andcrontabwith more secure versions. - Install
xntpfor accurate time stamping. - Consider enabling system accounting.
- Keep monitoring and testing the Web server.
Even if you only implement some of these security steps, your Web server will be much more secure than a standard server installed with a standard Unix configuration. But to be safe, go whole-hog and lock that server down with all of these tools and techniques.
5.1) Hardware setup
Don't connect the system to a network before it is installed and secured. Theoretically, some cracker could get in and drop back doors onto your system while you are in the process of securing it. There are documented cases of people trying to break into machines within five minutes of the machine being connected to the Internet.
You will need a CD-ROM drive to do the install and a tape or floppy drive for loading binaries and other files you created on other machines. These instructions are appropriate for Solaris 2.5. If you use a different OS version, the security of the resulting system may vary widely.
5.2) Install the OS
Start with the latest, solid version of Solaris 2.X. Each version of Solaris has been more secure than its predecessor.
Solaris is quite flexible and contains many conveniences that make your work easier. Unfortunately, all of this extra functionality also makes it easier for potential crackers to gain access to your system. When attempting to create a secure system, the best plan is to start with the simplest OS you can and then add packages one-by-one on an "as-needed" basis. A limited OS configuration also boots and runs faster and is less prone to crashing than a feature-rich version.
Under the Solaris install program, the most limited version of the OS you can select is the Core SPARC installation cluster. In fact, even this cluster has too many features. This cluster is what you should first install on your secure server. After you have selected Core SPARC in the Sun installation screens, you will want to select Customizeand add the Terminal Information cluster which gives you support for commonly used terminal emulators (such as
xterm and others).One of the advantages of the Core SPARC cluster is that it requires much less disk space than most types of Solaris installs. The following partition table is appropriate for machines loaded with the Core SPARC cluster:
s0: / 256 megabytes s1: swap 256 megabytes s2: overlap s3: s4: s5: s6: /local ??? megabytes (rest of the drive) s7:
/var is large to allow for keeping extra logging and auditing information. Size swap as appropriate for your hardware, but extra swap helps prevent "denial of service" type attacks.
Now, using some other machine, ftp to sunsolve.sun.com:/pub/patches and download the latest "recommended" (read: mandatory) patch cluster for Solaris 2.X (
2.X_Recommended.tar.Z). Put this tarfile on a tape, move it over to your secure server, and install the patches. Some patches will not be installed because the software they fix is not included in the Core SPARCcluster.5.3) Strip down the OS
Under Solaris, you control what processes are started at boot time by adding and removing files in /etc/rc[S0-3].d(the files in /etc/rc[S0-3].d being hard links to files in/etc/init.d). Many of these startup scripts run processes that you absolutely do not want running on your secure server: NFS is a prime example.
Consider removing all extraneous startup files from/etc/rc2.d. our advice and remove everything from/etc/init.d except the following files:
K15rrcd S05RMTMPFILES K15solved S20sysetup S72inetsvc S99audit S21perf S99dtlogin K25snmpd S30sysid.net S99netconfig S74syslog S75cron S92rtvc-config K60nfs.server K65nfs.client S69inet K92volmgt README S95SUNWmd.sync S01MOUNTFSYS S71sysid.sys S88utmpd S95rrcd
This list will be larger or smaller depending on if you have a graphics card in the machine, are using Solstice DiskSuite, and so on. Remove the files in /etc/rc3.d.
For Solaris 2.4, edit /etc/init.d/inetinit and add the following lines near the end of the file:
ndd -set /dev/ip ip_forward_directed_broadcasts 0 ndd -set /dev/ip ip_forward_src_routed 0 ndd -set /dev/ip ip_forwarding 0
These lines turn off a feature called IP forwarding. Nearly any machine that uses IP-based networking is capable of being a router, which means the bad guys could route packets through your machine to machines on your internal network or other secure machines that might trust the machine you are building. Turning off IP forwarding disables this feature. ```
Also consider setting the "ip_strict_dst_multihoming" kernel variable via
ndd -set /dev/ip ip_strict_dst_multihoming 1The solaris machine will then drop packets coming in through one interface that are destined for another interface. This can prevent host spoofing.
* Under Solaris 2.5, creating a file called /etc/notrouterwill turn off IP forwarding. To allow routing again, simply remove /etc/notrouter and reboot. It's important to note that there is a small time window between when this file is created and when routing is disabled, theoretically allowing some routing to take place.
Under Solaris 2.4, add a new script called/etc/init.d/tmpfix:
#!/bin/sh #ident "@(#)tmpfix 1.0 95/08/14" if [ -d /tmp ] then /usr/bin/chmod 1777 /tmp /usr/bin/chgrp sys /tmp /usr/bin/chown root /tmp
and then
ln /etc/init.d/tmpfix /etc/rc2.d/S79tmpfix so the script is invoked at boot time. This script prevents an attack that would allow a system cracker to get superuser access on your machine. It is not necessary under Solaris 2.5Some good advice from Casper Dik. Make sure that all of the startup routes run with the proper umask, so the files they create and not group or world writeable. Here's an easy method to insure this:
umask 022 # make sure umask.sh gets created with the proper mode
echo "umask 022" > /etc/init.d/umask.sh
for d in /etc/rc?.d
do
ln /etc/init.d/umask.sh $d/S00umask.sh
doneNote: the trailing ".sh" of the scriptname is important, if you don't specify it, the script will be executed in a sub-shell, not in the main shell that executes all other scripts.
Remove /etc/auto_*. Removing /etc/init.d/autofs should have prevented the automounter from starting up, but there's no reason to keep these files around either.
Remove /etc/dfs/dfstab. Again, purging /etc/init.d should prevent the machine from ever becoming an NFS server, but best to get rid of this file anyway.
Remove crontab files. You should remove all files from/var/spool/cron/crontabs except the
root file.Use static routing. Create an /etc/defaultrouter file instead of relying on information from
routed (which can be spoofed). If you need to route through different gateways, consider adding /usr/bin/route commands to/etc/init.d/inetinit instead of running routed.When you are done, reboot your machine. Always test boot file changes thoroughly. When the machine comes back up, the output of
ps -ef should look like this:UID PID PPID C STIME TTY TIME COMD
root 0 0 55 Mar 04 ? 0:01 sched
root 1 0 80 Mar 04 ? 22:44 /etc/init -
root 2 0 80 Mar 04 ? 0:01 pageout
root 3 0 80 Mar 04 ? 33:18 fsflush
root 9104 1 17 Mar 13 console 0:00 /usr/lib/saf/ttymon -g -h -p myhost console login: -T sun -d /dev/console -l co
root 92 1 80 Mar 04 ? 5:15 /usr/sbin/inetd -s
root 104 1 80 Mar 04 ? 21:53 /usr/sbin/syslogd
root 114 1 80 Mar 04 ? 0:11 /usr/sbin/cron
root 134 1 80 Mar 04 ? 0:01 /usr/lib/utmpd
root 198 1 25 Mar 04 ? 0:00 /usr/lib/saf/sac -t 300
root 201 198 33 Mar 04 ? 0:00 /usr/lib/saf/ttymon
root 6915 6844 8 13:03:32 console 0:00 ps -ef
root 6844 6842 39 13:02:04 console 0:00 -shYou will note that the /usr/lib/sendmail daemon is not running on the system: this is a feature. Processes that need to send mail off the system can and will invoke
sendmail directly (possibly via some other mail user agent such as mailx), but you do not have to run asendmail daemon that listens on port 25 and processes the mail queue immediately. You should add the following to root's crontab file:0 * * * * /usr/lib/sendmail -q > /var/adm/sendmail.log 2>&1
This entry will invoke
sendmail every hour to process any queued mail.5.4) Install third-party software
You will need three pieces of software to help secure your system and allow you to do safe administration of the machine over the network. Because there should be no compiler on your secure server, you will have to build these packages on some other machine and bring them onto the new machine you are building via a tape or floppy disk.
The first package is the TCP Wrappers package written by Wietse Venema. Wietse's source code produces a small binary called
tcpd that can be used to control access to services (such as telnet and ftp) that are started out of /etc/inetd.conf. Access control can be performed on IP address, domain name, and a raft of other parameters, and tcpd can raise alarms via syslogor e-mail if unauthorized connection attempts are made.Next, configure S/Key for remote secure access.
If you plan to allow
ftp access to your secure server (whether anonymous or for administrative access), you need to get a copy of the WU-Archive ftp daemon. You must get version 2.4 or later since previous versions have major security holes. If you are going to grant administrative ftp access (as opposed to only anonymous ftp), you must hack S/Key support into theftp daemon binary. In the Crimelabs S/Key distribution you will find an skey/misc/ftpd.c file that demonstrates how to make a previous version of the WU-Archive ftpdaemon support S/Key. You will have to make the analogous changes to the v2.4 wu-ftpd source.Compile and install the binaries (
tcpd, wu-ftpd, andkeyinit, keysu, and keysh from the S/Key software) in/usr/local/bin. When compiling wu-ftpd you will have to specify configuration and logging directories: we recommend you put the configuration directory somewhere under /etc and the logfiles under /var (so they have plenty of room to grow).Use /noshell for all non-login accounts. Make /noshell be the login shell for all users except root and access. This shell disallows the login, while logging that a login attempt occurred. Crackers will never be able to get access through these accounts.
5.5) Limit network access to the system
When your secure machine eventually gets into position on the network, you will probably want to be able to use
telnet and ftp to access the machine. Note that you do not have to enable these services on your machine, making your machine that much more secure, but that means you will always have to log in on the console and move files on and off the machine using tape or floppy disk.The
telnet and ftp daemons are started by the inetdprocess. inetd's configuration file, /etc/inet/inetd.conf, contains many other services besides telnet and ftp, so it is best to simply remove this file and create a new one containing only the following lines:ftp stream tcp nowait root /usr/local/bin/tcpd /usr/local/bin/wu-ftpd telnet stream tcp nowait root /usr/local/bin/tcpd /usr/sbin/in.telnetd
Note that we are using
tcpd to control access to both of these services and are using the wu-ftpd binary instead of the ftp server that comes with Solaris. If you do not want to allow anybody to telnet or ftp to you system, then simply remove the appropriate line from inetd.conf, or remove the file altogether and inetd will not even be started at boot time.Access control for
tcpd is configured using the/etc/hosts.allow and /etc/hosts.deny files. tcpd looks athosts.allow first, so you can permit a few machines to have telnet or ftp access and then deny access to everybody else in hosts.deny (this is often called a "default deny" policy). Here is a sample hosts.allow file:ALL: 172.16.3.0/255.255.255.0
This would allow any user on any host on the 172.16.3.0 network to have access to all of the services (
telnetand ftp) on your machine. That user will still have to supply the appropriate password or S/Key response (see below). Always use IP addresses in the hosts.allow file, because hostname information can be spoofed (if you are using the Internet Domain Name Service, or some other name service such as NIS).Now we want to disallow access for everybody else. Put the following line into /etc/hosts.deny:
ALL: ALL: /usr/bin/mailx -s "%d: connection attempt from %c" root@mydomain.com
Not only does this deny access to all services from allhosts, it causes
tcpd to send an alarm via e-mail that somebody is trying to get access to the machine. Substitute the e-mail address of somebody who reads e-mail regularly for root@mydomain.com in the above line.Now you want
tcpd to log all accesses via syslog. Put the following line in /etc/syslog.conf:auth.auth.notice;auth.info /var/log/authlog
The white-space on the line above must be tabs, or
syslog will be unable to properly parse the file and no logging will happen. Note that the logging facility is a configurable parameter when building tcpd, but we recommend using AUTH, as opposed to any LOCAL* facilities.sendmail from cron you can also run the daemon without the -bd option. This will cause the daemon to be a queue-watcher only. We prefer not to have the daemon running (one less process to worry about on the system), but your mileage may vary.tcpd. The correct line isauth.info /var/log/authlogwhich will log all auth events with severity info and higher to /var/log/authlog. Don't forget that the whitespace in this entry must be tabs.
You will need the S/Key package for remote, secure access. (Part of the logdaemon toolset). S/Key is a one-time-only password mechanism. Instead of typing in your password over the network, the S/Key software will send you a challenge string, and you will compute a response on your local machine using the challenge and a secret password that you have memorized. If you send the proper response back, the S/Key software gives you access to the machine but the response you gave will never again be valid for getting access to the machine. This means that if somebody is using a packet sniffer, they cannot capture the response and use it to break into your machine. The S/Key software also comes with a version of the
su command that uses S/Key challenge/response to grant superuser access safely over the network.To begin using S/Key, create an account that uses/usr/local/bin/keysh as its login shell. You will login as this user with some reusable password of your choosing and then
keysh will force you to respond to an S/Key challenge before giving you a shell prompt.You should put
access:x:100:100:Access Account:/tmp:/usr/local/bin/keyshat the end of /etc/passwd and
access:*LK*:6445::::::at the end of /etc/shadow. Then use the
passwd accesscommand to set the password for user access. The password you choose here doesn't have to be a very good password, since you will be relying on keysh to provide the security for this account.Since /usr/local/bin/keysh is not a standard shell, you have to create an /etc/shells file with these lines in it:
/sbin/sh /usr/local/bin/keyshOnly users whose login shell is one of these two shells are allowed to access the machine.
Now create an codepty /etc/skeykeys file and make it mode 600 and owned by root:
touch /etc/skeykeys chmod 600 /etc/skeykeys chown root /etc/skeykeys chgrp root /etc/skeykeysUse the
keyinit access command to initialize the S/Key secret for user access. You have completed the S/Key setup for user access.You now want to allow the user access to use the
keysucommand to become superuser. First change the entry for group root in /etc/group:root::0:root,accessOnly users listed in this entry are allowed to become superuser using
keysu. Now you have to use thekeyinit root command to initialize the S/Key secret for the superuser. I recommend using a different secret word than you used for user access.At this point you may be tcodepted to simply remove/bin/su so that users are forced to use
keysu. Unfortunately, many scripts use /bin/su to start processes that do not require full superuser access. You should, however, chmod 500 /bin/su so that only the superuser can run this program.Note the implicit assumption that access is a group account shared by several administrators. You may feel more comfortable giving each administrator a separate account with a different S/Key secret so that you have a better audit trail. The downside to this approach is it creates more accounts that can have bad passwords on them and allow crackers to gain access. Decide what makes sense for your organization.
wu-ftpConfiguring
wu-ftpd is tricky, even for experts. When you compiled wu-ftpd, you specified a directory where the daemon will look for its configuration files. This configuration directory will contain a pid directory and three files. The ftpconversions file should be empty but it must exist. The ftpusers file should contain a list of all users in the machine's password file who should not be allowed to ftp into the system. This file should containevery user in the password file: we will add a user later who is allowed to ftp into the system. Most especially, root should always be in the ftpusers file.The last file in the configuration directory is the
ftpaccess file. Rather than go into full detail, here is a file that you can use if you do not want to allow anonymous ftp into your system, but do want some users to be able to upload files to the machine:class users real 172.16.3.* log commands real log transfers real inbound,outboundThis allows users to
ftp from any host on network 172.16.3.0 and from nowhere else (which is redundant if you are already using tcpd, but security in depth is a Good Thing). All commands and file transfers will be logged to the log file you specified when you compiled the daemon (which is why we recommended you put it in/var where it has plenty of space to grow).Configuring anonymous
ftp is beyond the scope of this FAQ, but be warned to be very careful, because it is easy to make a mistake and give away access to your system. Review the documentation that comes with wu-ftpd for information and pointers to other documents on anonymous ftp.5.8) Limit access to files and file systems
Download and use
fix-modes. The programs in this package clean up unsecure group permissions on some system files and directories.One way to thwart potential system crackers is to prevent them from running setuid programs on your machine. The steps you have already taken make it unlikely that anybody is going to get an unauthorized setuid program onto your machine, but a little paranoia never hurt anybody in the security business.
Use the
nosuid option in /etc/vfstab to prevent setuid programs from being executed on any of your UFS filesystems:/proc - /proc proc - no - fd - /dev/fd fd - no - swap - /tmp tmpfs - yes nosuid /dev/dsk/c0t3d0s1 - - swap - no - /dev/dsk/c0t3d0s0 /dev/rdsk/c0t3d0s0 / ufs 1 no remount,nosuid /dev/dsk/c0t3d0s4 /dev/rdsk/c0t3d0s4 /usr ufs 1 no ro /dev/dsk/c0t3d0s5 /dev/rdsk/c0t3d0s5 /var ufs 1 no nosuid /dev/dsk/c0t3d0s6 /dev/rdsk/c0t3d0s6 /local ufs 2 yes nosuidNote that /usr contains some setuid executables (not the least of which are the S/Key binaries in /usr/local/bin), so we mount it read-only instead of
nosuid. The root filesystem is mounted by the boot PROM, so it has to be remounted for the nosuid directive to take effect.You must not apply the
nosuid directive to the special filesystems. Note that TMPFS type filesystems (such as/tmp) can be mounted nosuid with no known ill effects.Reboot your system one last time and plug it into the network. Confirm that the following are true:
- You should be able to telnet and ftp to your secure server from the machines you configured
tcpdto allow. - Trying to access the machine from any other machine should result in a denial of access and an e-mail to the appropriate party.
- You should be able to login via telnet and ftp as user access, but not as root or any other user.
- User access should be able to/usr/local/bin/keysu to become superuser.
ps -efshould show very few processes; in particular,sendmailand the various NFS processes should not be running.touch /usr/FOOshould fail with an indication that the filesystem is read-only.- As the superuser, copy the
pscommand to /, making sure to preserve the setuid bit. access should not be able to get a process listing with/ps -ef. Remove the/psbinary when you are done.