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Vulnerability Note VU#787448OpenSSH fails to properly handle multiple identical blocks in a SSH packetOverviewOpenSSH fails to properly handle multiple identical blocks in a SSH packet. This vulnerability may cause a denial-of-service condition.I. DescriptionOpenSSH is an open source client and server implementation of the Secure Shell (SSH) protocol. OpenSSH includes a cyclic redundancy check (CRC) compensation attack detection function that produces a checksum on a block of data in a SSH packet. This function was introduced to defend against exploitation of CRC weaknesses in version 1 of the SSH protocol (see VU#13877). Multiple identical blocks contained within a SSH packet may trigger a computationally expensive operation within the CRC attack detector that can lead to a denial of service. According to the OpenSSH 4.4 release notes:[This vulnerability]...would cause sshd(8) to spin until the login grace time expired. II. ImpactA remote, unauthenticated attacker could cause a denial-of service condition by sending specially crafted packets to the OpenSSH server that would cause it to use excessive CPU time until a connection timeout occurs.III. SolutionUpgradeSee the systems affected section of this document for information about specific vendors. Users who compile OpenSSH from source are encouraged to update to the most recent version.
References
This issue was reported in the OpenSSH 4.4 release notes. OpenSSH credits Tavis Ormandy of the Google Security Team for reporting this issue. This document was written by Chris Taschner.
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