Nextcloud Server is a Nextcloud package that handles data storage. In versions prior to 19.0.13, 20.0.11, and 21.0.3, filenames where not escaped by default in controllers using `DownloadResponse`. When a user-supplied filename was passed unsanitized into a `DownloadResponse`, this could be used to trick users into downloading malicious files with a benign file extension. This would show in UI behaviours where Nextcloud applications would display a benign file extension (e.g. JPEG), but the file will actually be downloaded with an executable file extension. The vulnerability is patched in versions 19.0.13, 20.0.11, and 21.0.3. Administrators of Nextcloud instances do not have a workaround available, but developers of Nextcloud apps may manually escape the file name before passing it into `DownloadResponse`.
The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.
| Link | Tags |
|---|---|
| https://github.com/nextcloud/security-advisories/security/advisories/GHSA-3hjp-26x8-mhf6 | third party advisory |
| https://github.com/nextcloud/server/pull/27354 | third party advisory patch |
| https://hackerone.com/reports/1215263 | permissions required |
| https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/J63NBVPR2AQCAWRNDOZSGRY5II4WS2CZ/ | vendor advisory |
| https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BVZS26RDME2DYTKET5AECRIZDFUGR2AZ/ | vendor advisory |
| https://security.gentoo.org/glsa/202208-17 | third party advisory vendor advisory |