USN-809-1: GnuTLS vulnerabilities

19 August 2009

gnutls12, gnutls13, gnutls26 vulnerabilities

A security issue affects these releases of Ubuntu and its derivatives:

  • Ubuntu 9.04
  • Ubuntu 8.10
  • Ubuntu 8.04 LTS
  • Ubuntu 6.06 LTS

Software Description

  • gnutls26
  • gnutls13
  • gnutls12


Moxie Marlinspike and Dan Kaminsky independently discovered that GnuTLS did not properly handle certificates with NULL characters in the certificate name. An attacker could exploit this to perform a man in the middle attack to view sensitive information or alter encrypted communications. (CVE-2009-2730)

Dan Kaminsky discovered GnuTLS would still accept certificates with MD2 hash signatures. As a result, an attacker could potentially create a malicious trusted certificate to impersonate another site. This issue only affected Ubuntu 6.06 LTS and Ubuntu 8.10. (CVE-2009-2409)

USN-678-1 fixed a vulnerability and USN-678-2 a regression in GnuTLS. The upstream patches introduced a regression when validating certain certificate chains that would report valid certificates as untrusted. This update fixes the problem, and only affected Ubuntu 6.06 LTS and Ubuntu 8.10 (Ubuntu 8.04 LTS and 9.04 were fixed at an earlier date). In an effort to maintain a strong security stance and address all known regressions, this update deprecates X.509 validation chains using MD2 and MD5 signatures. To accomodate sites which must still use a deprected RSA-MD5 certificate, GnuTLS has been updated to stop looking when it has found a trusted intermediary certificate. This new handling of intermediary certificates is in accordance with other SSL implementations.

Original advisory details:

Martin von Gagern discovered that GnuTLS did not properly verify certificate chains when the last certificate in the chain was self-signed. If a remote attacker were able to perform a man-in-the-middle attack, this flaw could be exploited to view sensitive information. (CVE-2008-4989)

Update instructions

The problem can be corrected by updating your system to the following package versions:

Ubuntu 9.04
libgnutls26 - 2.4.2-6ubuntu0.1
Ubuntu 8.10
libgnutls26 - 2.4.1-1ubuntu0.4
Ubuntu 8.04 LTS
libgnutls13 - 2.0.4-1ubuntu2.6
Ubuntu 6.06 LTS
libgnutls12 - 1.2.9-2ubuntu1.7

To update your system, please follow these instructions:

In general, a standard system upgrade is sufficient to effect the necessary changes.