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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" [
<!ENTITY base CDATA "..">
<!ENTITY date "$FreeBSD: www/en/security/security.sgml,v 1.153 2004/04/03 15:54:16 nectar Exp $">
<!ENTITY title "FreeBSD Security Information">
<!ENTITY % includes SYSTEM "../includes.sgml"> %includes;
<!ENTITY advisories.html.inc SYSTEM "advisories.html.inc">
]>
<!-- $FreeBSD: www/en/security/security.sgml,v 1.153 2004/04/03 15:54:16 nectar Exp $ -->
<html>
&header;
<H2>Introduction</H2>
<P>This web page is designed to assist both new and experienced users
in the area of FreeBSD security. FreeBSD
takes security very seriously and is constantly working
on making the OS as secure as possible.</P>
<P>Here you will find additional information, or links to information,
on how to protect your system against various types of attack,
on whom to contact if you find a security-related bug, and so on. There is
also a section on the various ways that the systems programmer can
become more security conscious so that he is less likely to
introduce vulnerabilities.</P>
<H2>Table of Contents</H2>
<UL>
<LI><A HREF="#sec">Information about the FreeBSD Security Officer</A></LI>
<LI><A HREF="#pol">Information handling policies</A></LI>
<LI><A HREF="#adv">FreeBSD Security Advisories</A></LI>
<LI><A HREF="#ml">FreeBSD Security Mailing Lists Information</A></LI>
<LI><A HREF="#tat">FreeBSD Security Tips and Tricks</A></LI>
<LI><A HREF="#spg">Secure Programming Guidelines</A></LI>
<LI><A HREF="#misc">Other Related Security Information</A></LI>
</UL>
<A NAME=sec></A>
<H2>The FreeBSD Security Officer and the Security Officer Team</H2>
<P>To better coordinate information exchange with others in the security
community, FreeBSD has a focal point for security-related communications:
the FreeBSD Security Officer.</P>
<P>If you need to contact the FreeBSD Project about
a possible security issue, you should therefore <A
HREF="mailto:security-officer@FreeBSD.org">send mail to the Security
Officer</A> with a description of what you have found and the type of
vulnerability it represents.</P>
<p>In order that the FreeBSD Project may respond to vulnerability
reports in a timely manner, there are four members of the Security
Officer mail alias: the Security Officer, the Deputy Security Officer,
and two Core Team members. Therefore, messages sent to the
<a
href="mailto:security-officer@FreeBSD.org">&lt;security-officer@FreeBSD.org&gt;</a>
mail alias are currently delivered to:</p>
<table>
<tr valign="top">
<td>Jacques Vidrine <a
href="mailto:nectar@FreeBSD.org">&lt;nectar@FreeBSD.org&gt;</a></td>
<td>Security Officer</td>
</tr>
<tr valign="top">
<td>Chris Faulhaber <a
href="mailto:jedgar@FreeBSD.org">&lt;jedgar@FreeBSD.org&gt;</a></td>
<td>Deputy Security Officer</td>
</tr>
<tr valign="top">
<td>Robert Watson <a
href="mailto:rwatson@FreeBSD.org">&lt;rwatson@FreeBSD.org&gt;</a></td>
<td>FreeBSD Core Team member, Release Engineering liaison,<br>
TrustedBSD Project liaison, system security architecture expert</td>
</tr>
<tr valign="top">
<td>Warner Losh <a
href="mailto:imp@FreeBSD.org">&lt;imp@FreeBSD.org&gt;</a></td>
<td>FreeBSD Core Team liaison, Security Officer Emeritus</td>
</tr>
</table>
<p>The Security Officer is supported by the <a
href="mailto:security-team@FreeBSD.org">FreeBSD Security Team
&lt;security-team@FreeBSD.org&gt;</a>, a small group of committers
vetted by the Security Officer.</p>
<p>Please use the <a
href="ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/public_key.asc">Security
Officer PGP key</a> to encrypt your messages to the Security Officer
when appropriate.</p>
<a NAME="pol"></a>
<h2>Information handling policies</h2>
<p>As a general policy, the FreeBSD Security Officer favors full
disclosure of vulnerability information after a reasonable delay to
permit safe analysis and correction of a vulnerability, as well as
appropriate testing of the correction, and appropriate coordination
with other affected parties.</p>
<p>The Security Officer <em>will</em> notify one or more of the
<a href="mailto:admins@FreeBSD.org">FreeBSD Cluster Admins</a> of
vulnerabilities that put the FreeBSD Project's resources under
immediate danger.</p>
<p>The Security Officer may bring additional FreeBSD developers
or outside developers into discussion of a submitted security
vulnerability if their expertise is required to fully understand or
correct the problem. Appropriate discretion will be exercised to
minimize unnecessary distribution of information about the submitted
vulnerability, and any experts brought in will act in accordance of
Security Officer policies. In the past, experts have been brought
in based on extensive experience with highly complex components of
the operating system, including FFS, the VM system, and the network
stack.</p>
<p>If a FreeBSD release process is underway, the FreeBSD Release
Engineer may also be notified that a vulnerability exists, and its
severity, so that informed decisions may be made regarding the release
cycle and any serious security bugs present in software associated
with an up-coming release. If requested, the Security Officer will
not share information regarding the nature of the vulnerability with
the Release Engineer, limiting information flow to existence and
severity.</p>
<p>The FreeBSD Security Officer has close working relationships
with a number of other organizations, including third-party vendors
that share code with FreeBSD (the OpenBSD and NetBSD projects,
Apple, and other vendors deriving software from FreeBSD, as well
as the Linux vendor security list), as well as organizations
that track vulnerabilities and security incidents, such as CERT.
Frequently vulnerabilities may extend beyond the scope of the
FreeBSD implementation, and (perhaps less frequently) may have
broad implications for the global networking community. Under such
circumstances, the Security Officer may wish to disclose vulnerability
information to these other organizations: if you do not wish the
Security Officer to do this, please indicate so explicitly in any
submissions.</p>
<p>Submitters should be careful to explicitly document any special
information handling requirements.</p>
<p>If the submitter of a vulnerability is interested in a coordinated
disclosure process with the submitter and/or other vendors, this
should be indicated explicitly in any submissions. In the absence
of explicit requests, the FreeBSD Security Officer will select a
disclosure schedule that reflects both a desire for timely disclosure
and appropriate testing of any solutions. Submitters should be aware
that if the vulnerability is being actively discussed in public forums
(such as bugtraq), and actively exploited, the Security Officer may
choose not to follow a proposed disclosure timeline in order to
provide maximum protection for the user community.</p>
<p>Submitters should be aware that the FreeBSD Project is an open
source project, and source revision control information for every
change made to the FreeBSD source tree is publicly accessible. If a
disclosure schedule is provided, it should take into account both the
official release of advisory, patch, and update information, as well
as initial inclusion of fixes in the FreeBSD source tree. There is
necessarily a lag between the inclusion of fixes in the tree and the
generation and releases of advisories, patches, and binary updates, as
the source control system is used to generate them.</p>
<p>Submissions may be protected using PGP. If desired, responses will
also be protected using PGP.</p>
<A NAME=adv></A>
<H2>FreeBSD Security Advisories</H2>
<P>The FreeBSD Security Officer provides security advisories for
several branches of FreeBSD development. These are the <EM>-STABLE
Branches</EM> and the <EM>Security Branches</EM>. (Advisories are not
issued for the <EM>-CURRENT Branch</EM>.)</P>
<UL>
<LI><P>There is usually only a single -STABLE branch, although
during the transition from one major development line to another
(such as from FreeBSD 4.x to 5.x), there is a time span in which
there are two -STABLE branches. The -STABLE branch tags have names
like <TT>RELENG_4</TT>. The corresponding builds have names like
<TT>FreeBSD 4.6-STABLE</TT>.</P></LI>
<LI><P>Each FreeBSD Release has an associated Security Branch.
The Security Branch tags have names like <TT>RELENG_4_6</TT>.
The corresponding builds have names like <TT>FreeBSD
4.6-RELEASE-p7</TT>.</P></LI>
</UL>
<P>Issues affecting the FreeBSD Ports Collection are covered
in <A HREF="http://vuxml.FreeBSD.org/">the FreeBSD VuXML
document</A>.</P>
<P>Each branch is supported by the Security Officer for a limited time
only, and is designated as one of `<EM>Early adopter</EM>',
`<EM>Normal</EM>', or `<EM>Extended</EM>'. The designation is used as a
guideline for determining the lifetime of the branch as follows.</P>
<DL>
<DT>Early adopter</DT>
<DD>Releases which are published from the -CURRENT branch will be
supported by the Security Officer for a minimum of 6 months after
the release.</DD>
<DT>Normal</DT>
<DD>Releases which are published from the -STABLE branch will be
supported by the Security Officer for a minimum of 12 months after the
release.</DD>
<DT>Extended</DT>
<DD>Selected releases will be supported by the Security Officer for a
minimum of 24 months after the release.</DD>
</DL>
<P>The current designation and estimated lifetimes of the currently
supported branches are given below. The <EM>Estimated EoL
(end-of-life)</EM> column gives the earliest date on which that branch
is likely to be dropped. Please note that these dates may be extended
into the future, but only extenuating circumstances would lead to a
branch's support being dropped earlier than the date listed.</P>
<TABLE BORDER="3" CELLSPACING="0" CELLPADDING="2">
<TR>
<TH>Branch</TH>
<TH>Release</TH>
<TH>Type</TH>
<TH>Estimated EoL</TH>
</TR>
<TR>
<TD>RELENG_4</TD>
<TD>n/a</TD>
<TD>n/a</TD>
<TD>March 31, 2005</TD>
</TR>
<TR>
<TD>RELENG_4_8</TD>
<TD>4.8-RELEASE</TD>
<TD>Extended</TD>
<TD>March 31, 2005</TD>
</TR>
<TR>
<TD>RELENG_5_2</TD>
<TD>5.2.1-RELEASE</TD>
<TD>Early adopter</TD>
<TD>December 31, 2004</TD>
</TR>
<TR>
<TD>RELENG_4_9</TD>
<TD>4.9-RELEASE</TD>
<TD>Normal</TD>
<TD>October 31, 2004</TD>
</TR>
</TABLE>
<P>Older releases are not maintained and users are strongly encouraged
to upgrade to one of the supported releases mentioned above.</P>
<P>Like all development efforts, security fixes are first brought into
the <A HREF="../doc/en_US.ISO8859-1/books/handbook/cutting-edge.html#CURRENT">FreeBSD-current</A> branch.
After a couple of days and some testing, the fix is retrofitted into
the supported FreeBSD-stable branch(es) and an advisory is then sent
out.</P>
<P>Some statistics about advisories released during 2002:</P>
<UL>
<LI>44 advisories of varying severity were issued for the base system.</LI>
<LI>12 advisories described vulnerabilities found only in FreeBSD.
The remaining 32 were problems shared with at least one other OS
(often due to shared code).</LI>
<LI>6 security notices were issued, covering a total of 95 issues in
optional third party applications included in the Ports Collection.</LI>
</UL>
<P>Advisories are sent to the following FreeBSD mailing lists:</P>
<UL>
<LI>FreeBSD-security-notifications@FreeBSD.org</LI>
<LI>FreeBSD-security@FreeBSD.org</LI>
<LI>FreeBSD-announce@FreeBSD.org</LI>
</UL>
<P>Advisories are always signed using the FreeBSD Security Officer
<A HREF="ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/public_key.asc"> PGP key
</A> and are archived, along with their associated patches, at our
<A HREF="ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/index.html">FTP CERT
repository</A>. At the time of this writing, the following advisories are
currently available (note that this list may be a few days out of date -
for the very latest advisories please check the
<A HREF="ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/advisories/">FTP site</A>):</P>
&advisories.html.inc;
<A NAME=ml></A>
<H2>FreeBSD Security Mailing Lists Information</H2>
<P>If you are administering or using any number of FreeBSD systems, you
should probably be subscribed to one or more of the following lists:</P>
<TABLE>
<TR>
<TD><A HREF="http://lists.FreeBSD.org/mailman/listinfo/freebsd-security">freebsd-security</A></TD>
<TD>General security related discussion</TD>
</TR>
<TR>
<TD><A HREF="http://lists.FreeBSD.org/mailman/listinfo/freebsd-security-notifications">freebsd-security-notifications</A></TD>
<TD>Security notifications (low-volume moderated list)</TD>
</TR>
</TABLE>
<A NAME=spg></A>
<H2>Secure Programming Guidelines</H2>
<P></P><UL>
<LI>Never trust any source of input, i.e. command line arguments,
environment variables, configuration files, incoming TCP/UDP/ICMP packets,
hostname lookups, function arguments, etc. If the length of or contents of
the data received is at all subject to outside control, then the program or
function should watch for this when copying it around. Specific security
issues to watch for in this are:
<P></P>
<UL>
<LI>strcpy() and sprintf() calls from unbounded data. Use strncpy and
snprintf() when the length is known (or implement some other form of
bounds-checking when the length is unknown). In fact, never ever use
gets() or sprintf(), period. If you do - we will send evil dwarfs after you.
<P></P></LI>
<LI>If you have to check the user input so it does not contain bad
characters of some sort, do NOT check for those bad characters. Instead
simply verify that it consists ONLY of those characters that you do
allow. In general concept is: disallow anything that is not
explicitly allowed.
<P></P></LI>
<LI>Read man pages for strncpy() and strncat() calls. Be sure to
understand how they work!!! While strncpy() might not append a terminating
\0, strncat() on the other hand adds the \0.
<P></P></LI>
<LI>Watch for strvis() and getenv() abuse. With strvis() it is easy to get
the destination string wrong, and getenv() can return strings much
longer then the program might expect. These two functions are one of the
key ways an attack is often made on a program, causing it to overwrite stack
or variables by setting its environment variables to unexpected values. If
your program reads environment variables, be paranoid. Be very paranoid!
<P></P></LI>
<LI>Ever time you use open() or stat() call - ask yourself: "What if it
is a symbolic link?"
<P></P></LI>
<LI>Make sure to use mkstemp() instead of mktemp(), tempnam(), etc.
Also make sure to look for races in /tmp in general, being aware that
there are very few things which can be atomic in /tmp:
<UL>
<LI>Creating a directory. This will either succeed or fail.</LI>
<LI>Opening a file O_CREAT | O_EXCL</LI>
</UL>
If you use mkstemp() the above cases will be properly handled for you. Hence
all temp files should use mkstemp() to guarantee there is not race
condition and that the permissions are correct.
<P></P></LI>
<LI>If an attacker can force packets to go/come from another arbitrary
system then that attacker has complete control over the data that we get
and <B>NONE</B> of it should be trusted.
<P></P></LI>
<LI>Never trust a configuration file is correctly formatted or that it was
generated by the appropriate utility. Don't trust user input such as
terminal names or language strings to be free of '/' or '../../../' if
there is any chance that they can be used in a path name. Don't trust
<B>ANY</B> paths supplied by the user when you are running setuid root.
<P></P></LI>
<LI>Look for holes or weaknesses in how data is stored. All temp files
should have 600 permission in order to be protected from prying eyes.
<P></P></LI>
<LI>Do not just grep for the usual suspects in programs which run with
elevated privileges. Look line by line for possible overflows in these
cases since there are a lot more ways to cause buffer overflows than
by abusing strcpy() and friends.
<P></P></LI>
<LI>Just because you drop privileges somewhere, it does not mean that no
exploit is possible. The attacker may put the necessary code on the
stack to regain the privileges before executing /bin/sh.</LI></UL>
<P></P></LI>
<LI>Do uid management. Do drop privileges as soon as possible, and really
do drop them. Switching between euid and uid is NOT enough. Use setuid()
when you can.
<P></P></LI>
<LI>Never display configuration file contents on errors. A line number and
perhaps position count is enough. This is true for all libs and for any
suid/sgid program.
<P></P></LI>
<LI>Tips for those reviewing existing code for security problems:<P></P><UL>
<LI>If you are unsure of your security fixes, send them to a reviewer with
whom you already have arrangements for a second glance over your
code. Don't commit code you are not sure about since breaking something
in the name of a security fix is rather embarrassing.
<P></P></LI>
<LI>Those without CVS commit privileges should make sure that a reviewer
with such privileges is among the last to review the changes. That person
will both review and incorporate the final version you would like to have
go into the tree.
<P></P></LI>
<LI>When sending changes around for review, always use context or unidiff
format diffs - this way diffs can be easily fed to patch(1). Do not simply
send the whole files. Diffs are much easier to read and apply to local
sources (especially those in which multiple, simultaneous changes may be
taking place). All changes should be relative to the -current branch of
development.
<P></P></LI>
<LI>Always directly test your changes (e.g. build and run the affected
sources) before sending them to a reviewer. Nobody likes being sent
obviously broken stuff for review, and it just makes it appear as though
the submitter didn't even really look at what he was submitting
(which is also hardly
confidence building). If you need accounts on a machine with a specific
version which you don't have available - just ask. The project has
resources available for exactly such purposes.
<P></P></LI>
<LI>Note for committers: do not forget to retrofit -current patches into
the -stable branch as appropriate.
<P></P></LI>
<LI>Do not needlessly rewrite code to suit your style/tastes - it only
makes the reviewer's job needlessly more difficult. Do so only if there
are clear reasons for it.</LI></UL>
<P></P></LI>
<LI>Look out for programs doing complex things with signal
handlers. Many routines in the various libraries are not sufficiently
reentrant to make this safe.
<P></P></LI>
<LI>Pay special attention to realloc() usage - more often then not the
function is not used correctly.
<P></P></LI>
<LI>When using fixed size buffers, use sizeof() to prevent lossage
when a buffer size is changed but the code which uses it isn't. For
example:
<pre>
char buf[1024];
struct foo { ... };
...
BAD:
xxx(buf, 1024)
xxx(yyy, sizeof(struct foo))
GOOD:
xxx(buf, sizeof(buf))
xxx(yyy, sizeof(yyy))
</pre>
Be careful though with sizeof of pointers when you really want the size
of where it points to!
<P></P></LI>
<LI>Every time you see "char foo[###]", check every usage of foo to make
sure that it can't be overflowed. If you can't avoid overflow (and cases
of this have been seen), then at least malloc the buffer so that one can't
walk on the stack.
<P></P></LI>
<LI>Always close file descriptors as soon as you can - this makes it more
likely that the stdio buffer contents will be discarded. In library
routines, always set any file descriptors that you open to close-on-exec.
<P></P></LI>
</UL>
<P>A useful auditing tool is the its4 port, located in
/usr/ports/security/its4/. This is an automated C code auditor which
highlights potential trouble-spots in the code. It is a useful
first-pass tool, but should not be relied upon as being authoritative,
and a complete audit should include human examination of the entire
code.</P>
<P>For more information on secure programming techniques and resources, see
the <A HREF="http://www.shmoo.com/securecode/">How to Write Secure Code</A>
resource center.</P>
<A NAME=tat></A>
<H2>FreeBSD Security Tips and Tricks</H2>
<P>There are several steps one must take to secure a FreeBSD system, or
in fact any &unix; system:</P>
<UL>
<LI>Disabling potentially dangerous software<BR><P></P>
A lot of software has to be run as a special privileged user to make
use of specific resources, by making the executable set-uid. An
example is UUCP or PPP software that makes use of a serial port, or
sendmail which has to write in the mail spool and bind to a privileged
network port. When you are not using UUCP, it is of little use to have
software on your system and it may be wise to disable it. Of course,
this requires good knowledge of what can be thrown away and what not,
as well as good indication whether or not you will want the functionality
in the future.<BR><P></P>
Also some utilities you may find not useful enough to have
around pose a possible security risk, like swapinfo. If you remove
the set-uid bit for the executable (via 'chmod ug-s filename' command)
you can always keep on using swapinfo when you're root. It is however
not a good idea to strip so many sbits that you have to be root all
the time.<BR><P></P>
Not only remove programs that you don't use, also remove services you
don't want or need to provide. This can be done by editing the
<TT>/etc/inetd.conf</TT> and <TT>/etc/rc.conf</TT> files and turning
off all services you don't use.<P></P></LI>
<LI>Fixing software which has security bugs (or how to stay one step ahead
of crackers)<BR><P></P>
Make sure you are subscribed to various <A HREF="#ml">FreeBSD Security
mailing lists</A> so you get updates on security bugs and
fixes. Apply the fixes immediately.<P></P></LI>
<LI>Backups - repair your system if a security breach does occur<BR><P></P>
Always have backups and a clean version of the operating system (e.g. on
CD-Rom).
Make sure your backups do not contain corrupted data or
data modified by attackers.<P></P></LI>
<LI>Install software to watch the state of the system<BR><P></P>
Programs like the tcp wrappers and tripwire (both in packages/ports) can
help you to monitor activity on your system. This makes it easier
to detect break-ins. Also read outputs of the /etc/security scripts
which are run daily and mailed to the root account.<P></P></LI>
<LI>Educating the people who work on the system<BR><P></P>
Users should know what they are doing. They should be told to never give
out their password to anyone and to also use hard-to-guess passwords.
Let them understand that the security of the system/network is partly
in their hands.<P></P></LI>
</UL>
<P>There is also a FreeBSD Security How-To available which provides some
advanced tips on how to improve security of your system. You can
find it at <A HREF="http://www.FreeBSD.org/~jkb/howto.html">
http://www.FreeBSD.org/~jkb/howto.html</A>.</P>
<P>Security is an ongoing process. Make sure you are following the latest
developments in the security arena.</P>
<A NAME=misc></A>
<H2>What to do when you detect a security compromise</H2>
<UL>
<LI><B>Determine the level of the security breach</B><BR>
What privileges did the attacker get? Did the attacker manage to get
root access? Did the attacker only manage to get user level access?</LI>
<LI><B>Determine if the state of system (kernel or userland) has been
tampered with</B><BR>
What software has been tampered with? Was new kernel installed? Were any
of the system binaries (such as telnetd, login, etc) modified? If you
believe an attacker could have done any tampering with an OS, you may want
to re-install the operating system from a safe medium.</LI>
<LI><B>Find out how the break-in was done</B><BR>
Did the break-in occur via a well-known security bug? If that is the case,
make sure to install the correct patches. Was the break-in successful due
to a misconfiguration? Was the break-in result of a new bug? If you believe
the break-in occurred via a new bug, you should warn the
<A HREF="mailto:security-officer@FreeBSD.org"> FreeBSD Security
Officer</A>.</LI>
<LI><B>Fix the security hole</B><BR>
Install new software or apply patches to the old one in order to fix the
problems. Disable any compromised accounts.</LI>
<LI><B>Other resources</B><BR>
<A HREF="http://www.cert.org">CERT</A> also offers
<A HREF="http://www.cert.org/nav/recovering.html">detailed information</A>
on what steps to take in case of a system compromise.</LI>
</UL>
<H2>Other Related Security Information</H2>
<UL>
<LI><A href="http://www.cerias.purdue.edu/coast/archive/index.html">The COAST
archive</A> contains a huge collection of security related materials.</LI>
<LI><A href="http://www.cerias.purdue.edu/infosec/hotlist/">The Center for
Education and Research in Information Assurance and Security (CERIAS)</A>
is the place to start looking for security related materials.
It contains hundreds of useful security pointers. Everything you always
wanted to know about security... and more.</LI>
<LI>The various CERT teams such as <A href="http://www.cert.org">
http://www.cert.org</A> and <A href="http://www.auscert.org.au">
http://www.auscert.org.au</A>.</LI>
<LI>Mailing lists such as <A HREF="http://www.securityfocus.com/forums/bugtraq/intro.html">
Bugtraq</A> and <A HREF="http://list.nfr.com/forum/firewall-wizards.html">
Firewall Wizards</A>.</LI>
</UL>
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