Impact
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. (e.g. EXE)
Patches
It is recommended that the Nextcloud Server is upgraded to 19.0.13, 20.0.11 or 21.0.3
Workarounds
- As an administrator of a Nextcloud instance there is no known workaround.
- As an developer of a Nextcloud app, you can manually escape the filename before passing it into
DownloadResponse.
References
For more information
If you have any questions or comments about this advisory:
Impact
Filenames where not escaped by default in controllers using
DownloadResponse. When a user-supplied filename was passed unsanitized into aDownloadResponse, 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. (e.g. EXE)
Patches
It is recommended that the Nextcloud Server is upgraded to 19.0.13, 20.0.11 or 21.0.3
Workarounds
DownloadResponse.References
For more information
If you have any questions or comments about this advisory: