Session fixation vulnerability in the authentication library in TYPO3 4.0.0 through 4.0.9, 4.1.0 through 4.1.7, and 4.2.0 through 4.2.3 allows remote attackers to hijack web sessions via unspecified vectors related to (1) frontend and (2) backend authentication.
https://exchange.xforce.ibmcloud.com/vulnerabilities/48133
http://www.securityfocus.com/bid/33376
http://www.debian.org/security/2009/dsa-1711
http://typo3.org/teams/security/security-bulletins/typo3-sa-2009-001/