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openssh -- multiple vulnerabilities


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.



portaudit: openssh -- multiple vulnerabilities

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If you have found a vulnerability in a FreeBSD port not listed in the database, please contact the FreeBSD Security Officer. Refer to "FreeBSD Security Information" for more information.

Oliver Eikemeier <>