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GHSA-2r6j-862c-m2v2
No affected components available
Problem
Due to the lack of ensuring file extensions belong to configured allowed mime-types, attackers can upload arbitrary data with arbitrary file extensions - however, default fileDenyPattern successfully blocked files like .htaccess or malicious.php.
TYPO3 Extbase extensions, which implement a file upload and do not implement a custom TypeConverter to transform uploaded files into FileReference domain model objects are affected by the vulnerability as well, since the UploadedFileReferenceConverter of ext:form handles the file upload and will accept files of any mime-type which are persisted to the default location.
In any way, uploaded files are placed in the default location /fileadmin/user_upload/, in most scenarios keeping the submitted filename - which allows attackers to directly reference files, or even correctly guess filenames used by other individuals, disclosing this information.
No authentication is required 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.
Type converter UploadedFileReferenceConverter is not registered globally anymore and just handles uploaded files within the scope of the Form Framework. Guessable storage location has changed from /fileadmin/user_upload/form_<random-hash>/ to /fileadmin/form_uploads/<random-40-bit>. Allowed mime-types must match expected file extensions (e.g. application/pdf must be .pdf, and cannot be .html).
Extbase extensions, who rely on the global availability of the UploadedFileReferenceConverter must now implement a custom TypeConverter to handle file uploads or explicitly implement the ext:form UploadedFileReferenceConverter with appropriate setting for accepted mime-types.
Credits
Thanks to Sebastian Michaelsen, Marc Lindemann, Oliver Eglseder, Markus Volkmer, Jakob Kunzmann, Johannes Regner, Richie Lee who reported this issue, and to TYPO3 core & security team members Oliver Hader & Benni Mack, as well as TYPO3 contributor Ralf Zimmermann who fixed the issue.
References
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a low impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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