The jumpUrl (aka access tracking) implementation in tslib/class.tslib_fe.php in TYPO3 4.2.x before 4.2.15, 4.3.x before 4.3.7, and 4.4.x before 4.4.4 does not properly compare certain hash values during access-control decisions, which allows remote attackers to read arbitrary files via unspecified vectors.
http://www.securityfocus.com/bid/43786
http://www.exploit-db.com/exploits/15856
http://www.debian.org/security/2010/dsa-2121
http://typo3.org/teams/security/security-bulletins/typo3-sa-2010-020/
http://blog.nibblesec.org/2010/12/typo3-sa-2010-020-typo3-sa-2010-022.html