OpenSSL, probably 0.9.6, does not verify the Basic Constraints for an intermediate CA-signed certificate, which allows remote attackers to spoof the certificates of trusted sites via a man-in-the-middle attack, a related issue to CVE-2002-0970.
http://www.blackhat.com/html/bh-dc-09/bh-dc-09-speakers.html#Marlinspike