It has been discovered that TYPO3 is susceptible to session fixation. If a user authenticates while anonymous session data is present, the session id is not changed. This makes it possible for attackers to generate a valid session id, trick users into using this session id (e.g. by leveraging a different Cross-Site Scripting vulnerability) and then maybe getting access to an authenticated session.

References

• TYPO3/typo3@4c9aba9
• TYPO3/typo3@4f6e84b
• https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms/2015-07-01-2.yaml
• https://typo3.org/security/advisory/typo3-core-sa-2015-003
• https://typo3.org/teams/security/security-bulletins/typo3-core/typo3-core-sa-2015-003