GnuPG is a popular open source signing and encryption tool.
Two flaws have been found in GnuPG 1.2.3.
First, ElGamal signing keys can be compromised. These keys are not commonly used, but this is "a significant security failure which can lead to a compromise of almost all ElGamal keys used for signing. Note that this is a real world vulnerability which will reveal your private key within a few seconds".
Second, there is a format string flaw in the 'gpgkeys_hkp' utility which "would allow a malicious keyserver in the worst case to execute an arbitrary code on the user's machine."
If you have used ElGamal keys for signing your private key can be compromised, and a malicious keyserver could remotely execute arbitrary code with the permissions of the user running gpgkeys_hkp.
There is no known workaround at this time.
All users who have created ElGamal signing keys should immediately revoke them. In addition, all Gentoo Linux machines with gnupg installed should be updated to use gnupg-1.2.3-r5 or higher:
# emerge sync
# emerge -pv '>=app-crypt/gnupg-1.2.3-r5'
# emerge '>=app-crypt/gnupg-1.2.3-r5'
# emerge clean