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.
ftp://patches.sgi.com/support/free/security/advisories/20040202-01-U.asc
distro.conectiva.com.br/atualizacoes/?id=a&anuncio=000798
lists.gnupg.org/pipermail/gnupg-announce/2003q4/000276.html
lists.gnupg.org/pipermail/gnupg-announce/2003q4/000277.html
marc.info/?l=bugtraq&m=106995769213221&w=2
secunia.com/advisories/10304
secunia.com/advisories/10349
secunia.com/advisories/10399
secunia.com/advisories/10400
www.debian.org/security/2004/dsa-429
www.kb.cert.org/vuls/id/940388
www.mandriva.com/security/advisories?name=MDKSA-2003:109
www.novell.com/linux/security/advisories/2003_048_gpg.html
www.redhat.com/support/errata/RHSA-2003-390.html
www.redhat.com/support/errata/RHSA-2003-395.html
www.securityfocus.com/bid/9115
oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10982