crypto/bn/bn_nist.c in OpenSSL before 0.9.8h on 32-bit platforms, as used in stunnel and other products, in certain circumstances involving ECDH or ECDHE cipher suites, uses an incorrect modular reduction algorithm in its implementation of the P-256 and P-384 NIST elliptic curves, which allows remote attackers to obtain the private key of a TLS server via multiple handshake attempts.
https://bugzilla.redhat.com/show_bug.cgi?id=757909
http://www.debian.org/security/2012/dsa-2390
http://rt.openssl.org/Ticket/Display.html?id=1593&user=guest&pass=guest
http://openwall.com/lists/oss-security/2011/12/01/6
http://marc.info/?t=119271238800004
http://eprint.iacr.org/2011/633
http://cvs.openssl.org/filediff?f=openssl/crypto/bn/bn_nist.c&v1=1.14&v2=1.21