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FreeBSD-SA-06:22.opensshSecurity Advisory
The FreeBSD Project
Topic: Multiple vulnerabilities in OpenSSH
Category: contrib
Module: openssh
Announced: 2006-09-30
Credits:Tavis Ormandy, Mark Dowd
Affects:All FreeBSD releases.
Corrected: 2006-09-30 19:50:57 UTC (RELENG_6, 6.2-PRERELEASE)
2006-09-30 19:51:56 UTC (RELENG_6_1, 6.1-RELEASE-p10)
2006-09-30 19:53:21 UTC (RELENG_6_0, 6.0-RELEASE-p15)
2006-09-30 19:54:03 UTC (RELENG_5, 5.5-STABLE)
2006-09-30 19:54:58 UTC (RELENG_5_5, 5.5-RELEASE-p8)
2006-09-30 19:55:52 UTC (RELENG_5_4, 5.4-RELEASE-p22)
2006-09-30 19:56:38 UTC (RELENG_5_3, 5.3-RELEASE-p37)
2006-09-30 19:57:15 UTC (RELENG_4, 4.11-STABLE)
2006-09-30 19:58:07 UTC (RELENG_4_11, 4.11-RELEASE-p25)
CVE Name: CVE-2006-4924, CVE-2006-5051
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
OpenSSH is an implementation of the SSH protocol suite, providing an
encrypted, authenticated transport for a variety of services,
including remote shell access.
II. Problem Description
The CRC compensation attack detector in the sshd(8) daemon, upon receipt
of duplicate blocks, uses CPU time cubic in the number of duplicate
blocks received. [CVE-2006-4924]
A race condition exists in a signal handler used by the sshd(8) daemon
to handle the LoginGraceTime option, which can potentially cause some
cleanup routines to be executed multiple times. [CVE-2006-5051]
III. Impact
An attacker sending specially crafted packets to sshd(8) can cause a
Denial of Service by using 100% of CPU time until a connection timeout
occurs. Since this attack can be performed over multiple connections
simultaneously, it is possible to cause up to MaxStartups (10 by default)
sshd processes to use all the CPU time they can obtain. [CVE-2006-4924]
The OpenSSH project believe that the race condition can lead to a Denial
of Service or potentially remote code execution, but the FreeBSD Security
Team has been unable to verify the exact impact. [CVE-2006-5051]
IV. Workaround
The attack against the CRC compensation attack detector can be avoided
by disabling SSH Protocol version 1 support in sshd_config(5).
There is no workaround for the second issue.
V. Solution
Perform one of the following:
1) Upgrade your vulnerable system to 4-STABLE, 5-STABLE, or 6-STABLE,
or to the RELENG_6_1, RELENG_6_0, RELENG_5_5, RELENG_5_4, RELENG_5_3,
or RELENG_4_11 security branch dated after the correction date.
2) To patch your present system:
The following patches have been verified to apply to FreeBSD 4.11, 5.3,
5.4, 5.5, 6.0, and 6.1 systems.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
[FreeBSD 4.11]
# fetch http://security.FreeBSD.org/patches/SA-06:22/openssh4x.patch
# fetch http://security.FreeBSD.org/patches/SA-06:22/openssh4x.patch.asc
[FreeBSD 5.x]
# fetch http://security.FreeBSD.org/patches/SA-06:22/openssh5x.patch
# fetch http://security.FreeBSD.org/patches/SA-06:22/openssh5x.patch.asc
[FreeBSD 6.x]
# fetch http://security.FreeBSD.org/patches/SA-06:22/openssh6x.patch
# fetch http://security.FreeBSD.org/patches/SA-06:22/openssh6x.patch.asc
b) Execute the following commands as root:
# cd /usr/src
# patch /path/to/patch
# cd /usr/src/secure/lib/libssh
# make obj make depend make make install
# cd /usr/src/secure/usr.sbin/sshd
# make obj make depend make make install
c) Restart the SSH daemon. On FreeBSD 5.x and 6.x, this can be done via
# /etc/rc.d/sshd restart
VI. Correction details
The following list contains the revision numbers of each file that was
corrected in FreeBSD.
Branch Revision
Path
- -
RELENG_4
src/crypto/openssh/deattack.c 1.1.1.1.2.6
src/crypto/openssh/deattack.h 1.1.1.1.2.3
src/crypto/openssh/defines.h1.1.1.2.2.3
src/crypto/openssh/log.c1.1.1.1.2.6
src/crypto/openssh/log.h1.1.1.1.2.4
src/crypto/openssh/packet.c 1.1.1.1.2.7
src/crypto/openssh/ssh_config 1.2.2.10
src/crypto/openssh/ssh_config.5 1.4.2.6
src/crypto/openssh/sshd.c 1.6.2.12
