Software Engineering Institute

GNU Privacy Guard (GnuPG) is the GNU project's implementation of the OpenPGP standard as defined by RFC2440.

OpenPGP messages are processed by GnuPG using data structures called filters that are used in a way similar to pipelines in the shell. Context structures that are usually allocated on the stack and passed to the filter functions are used for communications between these filters. Before the context structure gets deallocated, the OpenPGP data stream that is fed into the filters is closed. In some cases, while decrypting encrypted packets, this may not happen and the filter may use a void context structure filled with garbage that is under the attacker's control. Another context is included in the filter context for use by the low-level decryption. The decryption algorithm is accessed by this context via a function pointer.

According to GnuPG:
Using malformed OpenPGP packets an attacker is able to modify and dereference a function pointer in GnuPG.

The GnuPG advisory notes that both encrypted and signed data could be used as attack vectors for this vulnerability.

A remote, unauthenticated attacker with the ability to supply specially crafted OpenPGP packets to a vulnerable version of GnuPG may be able to execute arbitrary code on an affected system. The attacker-supplied code would be executed with the privileges of the user or application invoking gpg.

Apply a patch or upgrade

Patches have been released to address this issue. Please see the Systems Affected section of this document for more details on specific vendors.

Users who compile GnuPG from the original distribution are encouraged to upgrade to version 1.4.6 (or later) or apply the patch to upgrade from 1.4.5 to 1.4.6.

Run with limited privileges

Running GnuPG with reduced privileges may help mitigate the effects of this vulnerability. Note that this workaround will not prevent exploitation.