Executive brief
TYPO3's Form Framework is used to create and manage web forms on websites. This vulnerability allows attackers to upload files with arbitrary MIME types to forms that have file upload fields, bypassing the intended file type restrictions. While PHP files cannot be uploaded, an attacker could upload other dangerous file types (such as SVG with embedded scripts or other executable formats) to compromise website integrity or inject malicious content.
Technical details
The vulnerability is a server-side validation bypass in TYPO3's Form Framework (CWE-351: Insufficient Type Distinction). The MimeTypeValidator is instantiated during form construction before concrete form definition properties (such as allowedMimeTypes restrictions) are applied to the form instance. As a result, the validator never participates in the form processing pipeline, allowing FileUpload and ImageUpload elements to accept files of any MIME type regardless of configured restrictions. The attack requires network access to a TYPO3 instance with affected form components but no authentication or user interaction beyond form submission. Although PHP execution is prevented by other mechanisms, attackers can still upload malicious file types to alter website content or deliver payloads. The fix is available in TYPO3 version 14.3.5 LTS and later.
Affected products
- TYPO3 CMS Form Framework 14.2.0 to 14.3.4
Timeline
- 2026-08-17: disclosed: Advisory published to GitHub
- 2026-08-31: patched: Fix released in TYPO3 14.3.5 LTS