Nikos Mavrogiannopoulos of Red Hat discovered an X.509 certificate verification issue in GnuTLS, an SSL/TLS library. A certificate validation could be reported sucessfully even in cases were an error would prevent all verification steps to be performed.

An attacker doing a man-in-the-middle of a TLS connection could use this vulnerability to present a carefully crafted certificate that would be accepted by GnuTLS as valid even if not signed by one of the trusted authorities.

For the oldstable distribution (squeeze), this problem has been fixed in version 2.8.6-1+squeeze3.

For the stable distribution (wheezy), this problem has been fixed in version 2.12.20-8+deb7u1.

For the testing distribution (jessie), this problem has been fixed in version 2.12.23-13.

For the unstable distribution (sid), this problem has been fixed in version 2.12.23-13.

We recommend that you upgrade your gnutls26 packages.