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Category:   Application (VPN)  >   OpenSSH Vendors:   OpenSSH.org
OpenSSH SSH v1 CRC Attack Detection Implementation Lets Remote Users Deny Service
SecurityTracker Alert ID:  1016931
SecurityTracker URL:  http://securitytracker.com/id/1016931
CVE Reference:   CVE-2006-4924   (Links to External Site)
Updated:  Sep 28 2006
Original Entry Date:  Sep 26 2006
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 4.3 and prior versions
Description:   A vulnerability was reported in OpenSSH. A remote user can cause denial of service conditions.

A remote user can cause the target OpenSSH service to consume excessive CPU resources when SSH protocol version 1 is enabled.

The flaw resides in the CRC attack detection function in the processing of identical blocks.

Tavis Ormandy of the Google Security Team discovered this vulnerability.

Impact:   A remote user can cause the target service to consume excessive CPU resources.
Solution:   The vendor has issued a fixed version (4.4).

The vendor has also issued the following source code fixes:

http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/deattack.c.diff?r1=1.29&r2=1.30&sortby=date&f=h
http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/packet.c.diff?r1=1.143&r2=1.144&sortby=date&f=h
http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/deattack.h.diff?r1=1.9&r2=1.10&sortby=date&f=h

The OpenSSH advisory is available at:

http://www.openssh.org/txt/release-4.4

Vendor URL:  www.openssh.org/ (Links to External Site)
Cause:   State error
Underlying OS:  Linux (Any), UNIX (Any)

Message History:   This archive entry has one or more follow-up message(s) listed below.
Sep 29 2006 (Red Hat Issues Fix) OpenSSH SSH v1 CRC Attack Detection Implementation Lets Remote Users Deny Service
Red Hat has released a fix for Red Hat Enterprise Linux 3 and 4.
Sep 29 2006 (Red Hat Issues Fix) OpenSSH SSH v1 CRC Attack Detection Implementation Lets Remote Users Deny Service
Red Hat has released a fix for Red Hat Enterprise Linux 2.1
Oct 12 2006 (OpenBSD Issues Fix) OpenSSH SSH v1 CRC Attack Detection Implementation Lets Remote Users Deny Service
OpenBSD has issued a fix.
Dec 5 2006 (HP Issues Fix for HP-UX Secure Shell) OpenSSH SSH v1 CRC Attack Detection Implementation Lets Remote Users Deny Service
HP has issued a fix for HP-UX Secure Shell.
Jun 11 2007 (Sun Issues Fix) OpenSSH SSH v1 CRC Attack Detection Implementation Lets Remote Users Deny Service
Sun has issued a fix for Solaris 9 and 10.
Mar 18 2009 (Blue Coat Issues Fix for ProxySG) OpenSSH SSH v1 CRC Attack Detection Implementation Lets Remote Users Deny Service
Blue Coat has issued a fix for ProxySG.



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