gnutls26 - missing bounds check

Matthew Hall discovered that GNUTLS does not properly handle truncated
GenericBlockCipher structures nested inside TLS records, leading to
crashes in applications using the GNUTLS library.

For the stable distribution (squeeze), this problem has been fixed in
version 2.8.6-1+squeeze2.

For the unstable distribution (sid), this problem has been fixed in
version 2.12.18-1 of the gnutls26 package and version 3.0.17-2 of the
gnutls28 package.

We recommend that you upgrade your gnutls26 packages.