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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2011.0120.2 A vulnerability has been identified in OpenSSH 14 February 2011 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: OpenSSH 5.6 OpenSSH 5.7 Publisher: OpenBSD Operating System: UNIX variants (UNIX, Linux, OSX) Impact/Access: Access Confidential Data -- Remote with User Interaction Resolution: Patch/Upgrade CVE Names: CVE-2011-0539 Original Bulletin: http://www.openssh.com/txt/legacy-cert.adv Revision History: February 14 2011: Added CVE reference February 7 2011: Initial Release - --------------------------BEGIN INCLUDED TEXT-------------------- OpenSSH Security Advisory: legacy-certs.adv This document may be found at: http://www.openssh.com/txt/legacy-cert.adv 1. Vulnerability Legacy certificates generated by OpenSSH might contain data from the stack thus leaking confidential information. 2. Affected configurations OpenSSH 5.6 and OpenSSH 5.7 only when generating legacy certificates. These must be specifically requested using the "-t" option on the ssh-keygen CA command-line. 3. Mitigation Avoid generating legacy certificates using OpenSSH 5.6 or 5.7 If legacy certificates have been issued with a vulnerable OpenSSH version, consider rotating any CA key used. 4. Details When generating legacy *-cert-v00@openssh.com certificates, the nonce field was not being correctly filled with random data but was left uninitialised, containing the contents of the stack. The contents of the stack at this point in ssh-keygen's execution do not appear to leak the CA private key or other sensitive data, but this possibility cannot be excluded on all platforms and library versions. If certificates are generated using user-specified contents (as opposed to the CA specifying all fields) then they will be less resistant to hash collision attacks. Fortunately, such attacks are not currently considered practical for the SHA family of hashes used to sign these certificates. 5. Credit This issue was privately reported by Mateusz Kocielski on January 26, 2011. 6. Fix OpenSSH 5.8 contains a fix for this vulnerability. Users who prefer to continue to use OpenSSH 5.6 or 5.7 may apply this patch: Index: key.c =================================================================== RCS file: /cvs/src/usr.bin/ssh/key.c,v retrieving revision 1.95 diff -u -r1.95 key.c - --- key.c 10 Nov 2010 01:33:07 -0000 1.95 +++ key.c 3 Feb 2011 06:52:33 -0000 @@ -1823,8 +1823,8 @@ buffer_put_cstring(&k->cert->certblob, key_ssh_name(k)); /* -v01 certs put nonce first */ + arc4random_buf(&nonce, sizeof(nonce)); if (!key_cert_is_legacy(k)) { - - arc4random_buf(&nonce, sizeof(nonce)); buffer_put_string(&k->cert->certblob, nonce, sizeof(nonce)); } _______________________________________________ - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/render.html?cid=1980 =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iD8DBQFNWJxN/iFOrG6YcBERAuxAAJ9YxZaIz89L1GVt92Z9wQOqvecABwCfatkC kHIhlDR9CQiooxQ0yAiEh5M= =tL/z -----END PGP SIGNATURE-----