FreeBSD VuXML: Documenting security issues in FreeBSD and the FreeBSD Ports Collection

openssh -- multiple vulnerabilities

Affected packages
6.1 <= FreeBSD < 6.1_10
6.0 <= FreeBSD < 6.0_15
5.5 <= FreeBSD < 5.5_8
5.4 <= FreeBSD < 5.4_22
5.0 <= FreeBSD < 5.3_37
FreeBSD < 4.11_25
openssh < 4.4,1
openssh-portable < 4.4.p1,1


VuXML ID 32db37a5-50c3-11db-acf3-000c6ec775d9
Discovery 2006-09-25
Entry 2006-09-30

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]


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]


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.


Bugtraq ID 20216
CVE Name CVE-2006-4924
CVE Name CVE-2006-5051
FreeBSD Advisory SA-06:22.openssh