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Posted on 23 December 2011
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FreeBSD-SA-11:08.telnetd Security Advisory
The FreeBSD Project
Topic: telnetd code execution vulnerability
Category: core
Module: contrib
Announced: 2011-12-23
Affects: All supported versions of FreeBSD.
Corrected: 2011-12-23 15:00:37 UTC (RELENG_7, 7.4-STABLE)
2011-12-23 15:00:37 UTC (RELENG_7_4, 7.4-RELEASE-p5)
2011-12-23 15:00:37 UTC (RELENG_7_3, 7.3-RELEASE-p9)
2011-12-23 15:00:37 UTC (RELENG_8, 8.2-STABLE)
2011-12-23 15:00:37 UTC (RELENG_8_2, 8.2-RELEASE-p5)
2011-12-23 15:00:37 UTC (RELENG_8_1, 8.1-RELEASE-p7)
2011-12-23 15:00:37 UTC (RELENG_9, 9.0-STABLE)
2011-12-23 15:00:37 UTC (RELENG_9_0, 9.0-RELEASE)
CVE Name: CVE-2011-4862
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.
I. Background
The FreeBSD telnet daemon, telnetd(8), implements the server side of the
TELNET virtual terminal protocol. It has been disabled by default in
FreeBSD since August 2001, and due to the lack of cryptographic security
in the TELNET protocol, it is strongly recommended that the SSH protocol
be used instead. The FreeBSD telnet daemon can be enabled via the
/etc/inetd.conf configuration file and the inetd(8) daemon.
The TELNET protocol has a mechanism for encryption of the data stream
(but it is not cryptographically strong and should not be relied upon
in any security-critical applications).
II. Problem Description
When an encryption key is supplied via the TELNET protocol, its length
is not validated before the key is copied into a fixed-size buffer.
III. Impact
An attacker who can connect to the telnetd daemon can execute arbitrary
code with the privileges of the daemon (which is usually the "root"
superuser).
IV. Workaround
No workaround is available, but systems not running the telnet daemon
are not vulnerable.
Note that the telnet daemon is usually run via inetd, and consequently
will not show up in a process listing unless a connection is currently
active; to determine if it is enabled, run
$ ps ax | grep telnetd | grep -v grep
$ grep telnetd /etc/inetd.conf | grep -vE '^#'
If any output is produced, your system may be vulnerable.
V. Solution
Perform one of the following:
1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to the
RELENG_8_2, RELENG_8_1, RELENG_7_4, or RELENG_7_3 security branch dated
after the correction date.
2) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to FreeBSD 7.4, 7.3,
8.2, and 8.1 systems.
a) Download the patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch http://security.FreeBSD.org/patches/SA-11:08/telnetd.patch
# fetch http://security.FreeBSD.org/patches/SA-11:08/telnetd.patch.asc
b) Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/lib/libtelnet
# make obj && make depend && make && make install
# cd /usr/src/libexec/telnetd
# make obj && make depend && make && make install
3) To update your vulnerable system via a binary patch:
Systems running 7.4-RELEASE, 7.3-RELEASE, 8.2-RELEASE, or 8.1-RELEASE on
the i386 or amd64 platforms can be updated via the freebsd-update(8)
utility:
# freebsd-update fetch
# freebsd-update install
VI. Correction details
The following list contains the revision numbers of each file that was
corrected in FreeBSD.
CVS:
Branch Revision
Path
- -------------------------------------------------------------------------
RELENG_7
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.2.24.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.24.1
RELENG_7_4
src/UPDATING 1.507.2.36.2.7
src/sys/conf/newvers.sh 1.72.2.18.2.10
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.2.38.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.40.2
RELENG_7_3
src/UPDATING 1.507.2.34.2.11
src/sys/conf/newvers.sh 1.72.2.16.2.13
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.2.36.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.38.2
RELENG_8
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.3.2.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.36.2
RELENG_8_2
src/UPDATING 1.632.2.19.2.7
src/sys/conf/newvers.sh 1.83.2.12.2.10
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.3.8.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.36.1.6.2
RELENG_8_1
src/UPDATING 1.632.2.14.2.10
src/sys/conf/newvers.sh 1.83.2.10.2.11
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.3.6.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.36.1.4.2
RELENG_9
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.3.10.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.42.2
RELENG_9_0
src/crypto/heimdal/appl/telnet/libtelnet/encrypt.c 1.1.1.3.12.1
src/contrib/telnet/libtelnet/encrypt.c 1.9.42.1.2.2
- -------------------------------------------------------------------------
Subversion:
Branch/path Revision
- -------------------------------------------------------------------------
stable/7/ r228843
releng/7.4/ r228843
releng/7.3/ r228843
stable/8/ r228843
releng/8.2/ r228843
releng/8.1/ r228843
stable/9/ r228843
releng/9.0/ r228843
- -------------------------------------------------------------------------
VII. References
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-4862
The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-11:08.telnetd.asc
