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USN-809-1: GnuTLS vulnerabilities

19 August 2009

GnuTLS vulnerabilities




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 machine-in-the-middle attack
to view sensitive information or alter encrypted communications.

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

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 machine-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
Ubuntu 8.10
Ubuntu 8.04
Ubuntu 6.06

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

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