The _gnutls_x509_verify_certificate function in lib/x509/verify.c in libgnutls in GnuTLS before 2.6.1 trusts certificate chains in which the last certificate is an arbitrary trusted, self-signed certificate, which allows man-in-the-middle attackers to insert a spoofed certificate for any Distinguished Name (DN).
https://www.redhat.com/archives/fedora-package-announce/2008-November/msg00293.html
https://www.redhat.com/archives/fedora-package-announce/2008-November/msg00222.html
https://exchange.xforce.ibmcloud.com/vulnerabilities/46482
http://www.ubuntu.com/usn/usn-678-2
http://www.gnu.org/software/gnutls/security.html
http://www.debian.org/security/2009/dsa-1719
http://security.gentoo.org/glsa/glsa-200901-10.xml
http://lists.opensuse.org/opensuse-security-announce/2009-04/msg00010.html
http://lists.opensuse.org/opensuse-security-announce/2008-12/msg00002.html