The libCheckSignature function in crypto-utils.lib for OpenCA 0.9.1.6 and earlier only compares the serial of the signer's certificate and the one in the database, which can cause OpenCA to incorrectly accept a signature if the certificate's chain is trusted by OpenCA's chain directory, allowing remote attackers to spoof requests from other users.
https://exchange.xforce.ibmcloud.com/vulnerabilities/14847
http://www.securityfocus.com/bid/9435
http://www.openca.org/news/CAN-2004-0004.txt