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FreeBSD-SA-16:36.telnetd Security Advisory
The FreeBSD Project
Topic: Possible login(1) argument injection in telnetd(8)
Category: core
Module: telnetd
Announced: 2016-12-06
Credits: Brooks Davis (sponsored by: DARPA, AFRL)
Affects: All supported versions of FreeBSD.
Corrected: 2016-12-06 18:52:02 UTC (stable/11, 11.0-STABLE)
2016-12-06 18:49:38 UTC (releng/11.0, 11.0-RELEASE-p4)
2016-12-06 18:52:18 UTC (stable/10, 10.3-STABLE)
2016-12-06 18:49:48 UTC (releng/10.3, 10.3-RELEASE-p13)
2016-12-06 18:49:54 UTC (releng/10.2, 10.2-RELEASE-p26)
2016-12-06 18:49:59 UTC (releng/10.1, 10.1-RELEASE-p43)
2016-12-06 18:52:33 UTC (stable/9, 9.3-STABLE)
2016-12-06 18:50:06 UTC (releng/9.3, 9.3-RELEASE-p51)
CVE Name: CVE-2016-1888
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://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.
After a user is connected, telnetd executes the login(1) program or a
similar program specified by the -p <loginprog> argument. In order to do
so, it constructs an array of command line arguments which are passed to
execv(3).
II. Problem Description
An unexpected sequence of memory allocation failures combined with
insufficient error checking could result in the construction and
execution of an argument sequence that was not intended.
III. Impact
An attacker who controls the sequence of memory allocation failures and
success may cause login(1) to run without authentication and may be able
to cause misbehavior of login(1) replacements.
No practical way of controlling these memory allocation failures is
known at this time.
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 a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.
2) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:
# freebsd-update fetch
# freebsd-update install
3) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to the applicable
FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch https://security.FreeBSD.org/patches/SA-16:36/telnetd.patch
# fetch https://security.FreeBSD.org/patches/SA-16:36/telnetd.patch.asc
# gpg –verify telnetd.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.
Kill any running telnetd processes, or reboot the system.
VI. Correction details
The following list contains the correction revision numbers for each
affected branch.
Branch/path Revision
– ————————————————————————-
stable/9/ r309643
releng/9.3/ r309637
stable/10/ r309642
releng/10.1/ r309636
releng/10.2/ r309635
releng/10.3/ r309634
stable/11/ r309641
releng/11.0/ r309633
– ————————————————————————-
To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:
# svn diff -cNNNNNN –summarize svn://svn.freebsd.org/base
Or visit the following URL, replacing NNNNNN with the revision number:
<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
VII. References
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1888>
The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:36.telnetd.asc>
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