The System extension Install tool in TYPO3 4.0.0 through 4.0.9, 4.1.0 through 4.1.7, and 4.2.0 through 4.2.3 creates the encryption key with an insufficiently random seed, which makes it easier for attackers to crack the key.
https://exchange.xforce.ibmcloud.com/vulnerabilities/48132
http://www.debian.org/security/2009/dsa-1711
http://typo3.org/teams/security/security-bulletins/typo3-sa-2009-001/