A weakness and some vulnerabilities have been reported in libvirt, which can be exploited by malicious, local users in a guest system to bypass certain security restrictions.

1) Some vulnerabilities are caused due to libvirt e.g. incorrectly probing the disk format from data contained in the disk's header. This can be exploited by a malicious user in a guest system to e.g. read arbitrary files on the host by writing a fake header to a raw formatted disk image.

2) The bridge network driver generates potentially insecure iptables masquerading rules for NAT guests, which may allow access to network services intended to be restricted.

Solution
Fixed in the GIT repository.

Provided and/or discovered by
1) Red Hat
2) Red Hat credits Jeremy Nickurak

Changelog
Further details available to Secunia VIM customers

Original Advisory
1) http://permalink.gmane.org/gmane.comp.emulators.libvirt/26691
https://bugzilla.redhat.com/show_bug.cgi?id=607810
https://bugzilla.redhat.com/show_bug.cgi?id=607811
https://bugzilla.redhat.com/show_bug.cgi?id=607812
https://bugzilla.redhat.com/show_bug.cgi?id=709769
2) https://bugzilla.redhat.com/show_bug.cgi?id=602455

Other references
Further details available to Secunia VIM customers

Deep Links
Links available to Secunia VIM customers