Executive brief
The Mask extension for TYPO3 (a popular open-source content management system) fails to properly validate user-supplied template file names, allowing authenticated backend administrators to exploit path traversal sequences to create or delete HTML files outside the intended template directory. An attacker with legitimate backend access could manipulate file paths to overwrite critical system files or delete important templates, disrupting site operations or potentially compromising the integrity of the installation.
Technical details
The vulnerability is a path traversal (CWE-22) and improper path resolution (CWE-73) issue in the Mask extension's template file handling. When processing a client-supplied template element key, the extension fails to sanitize or validate the input before using it to construct file paths for saving and deleting .html template files. An authenticated backend user with access to the Mask module can supply a key containing sequences like "../" to traverse outside the configured template directory. The attack requires valid backend authentication and explicit access to the Mask module, limiting the exposure to trusted administrative users. Patch versions 8.3.12 and 9.0.11 have been released to address this issue.
Affected products
- TYPO3 Mask 8.3.11 and below, 9.0.0 - 9.0.10
Timeline
- 2026-08-25: disclosed
- 2026-08-25: patched: Versions 8.3.12 and 9.0.11 available