Problem

Due to improper input validation, attackers can by-pass restrictions of predefined options and submit arbitrary data in the Form Designer backend module of the Form Framework.

In the default configuration of the Form Framework this allows attackers to explicitly allow arbitrary mime-types for file uploads - however, default fileDenyPattern successfully blocked files like .htaccess or malicious.php. Besides that, attackers can persist those files in any writable directory of the corresponding TYPO3 installation.

A valid backend user account with access to the form module is needed to exploit this vulnerability.

Solution

Update to TYPO3 versions 8.7.40, 9.5.25, 10.4.14, 11.1.1 that fix the problem described.

Credits

Thanks to Richie Lee who reported this issue and to TYPO3 contributor Ralf Zimmermann who fixed the issue.

References

• TYPO3-CORE-SA-2021-003

References

• GHSA-3vg7-jw9m-pc3f
• https://packagist.org/packages/typo3/cms-form
• https://nvd.nist.gov/vuln/detail/CVE-2021-21357
• https://typo3.org/security/advisory/typo3-core-sa-2021-003
• https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms-core/CVE-2021-21357.yaml
• https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms/CVE-2021-21357.yaml