GnuPG (GPG) 1.0.2, and other versions up to 1.2.3, creates ElGamal type 20 (sign+encrypt) keys using the same key component for encryption as for signing, which allows attackers to determine the private key from a signature.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10982
http://www.securityfocus.com/bid/9115
http://www.redhat.com/support/errata/RHSA-2003-395.html
http://www.redhat.com/support/errata/RHSA-2003-390.html
http://www.novell.com/linux/security/advisories/2003_048_gpg.html
http://www.mandriva.com/security/advisories?name=MDKSA-2003:109
http://www.kb.cert.org/vuls/id/940388
http://www.debian.org/security/2004/dsa-429
http://secunia.com/advisories/10400
http://secunia.com/advisories/10399
http://secunia.com/advisories/10349
http://secunia.com/advisories/10304
http://marc.info/?l=bugtraq&m=106995769213221&w=2
http://lists.gnupg.org/pipermail/gnupg-announce/2003q4/000277.html
http://lists.gnupg.org/pipermail/gnupg-announce/2003q4/000276.html
http://distro.conectiva.com.br/atualizacoes/?id=a&anuncio=000798