Flatpak is a Linux application sandboxing and distribution framework. Prior to versions 1.12.3 and 1.10.6, Flatpak doesnt properly validate that the permissions displayed to the user for an app at install time match the actual permissions granted to the app at runtime, in the case that theres a null byte in the metadata file of an app. Therefore apps can grant themselves permissions without the consent of the user. Flatpak shows permissions to the user during install by reading them from the xa.metadata key in the commit metadata. This cannot contain a null terminator, because it is an untrusted GVariant. Flatpak compares these permissions to the actual metadata, from the metadata file to ensure it wasnt lied to. However, the actual metadata contents are loaded in several places where they are read as simple C-style strings. That means that, if the metadata file includes a null terminator, only the content of the file from before the terminator gets compared to xa.metadata. Thus, any permissions that appear in the metadata file after a null terminator are applied at runtime but not shown to the user. So maliciously crafted apps can give themselves hidden permissions. Users who have Flatpaks installed from untrusted sources are at risk in case the Flatpak has a maliciously crafted metadata file, either initially or in an update. This issue is patched in versions 1.12.3 and 1.10.6. As a workaround, users can manually check the permissions of installed apps by checking the metadata file or the xa.metadata key on the commit metadata.
During installation, installed file permissions are set to allow anyone to modify those files.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Flatpak | Flatpak | * | 1.10.6 (excluding) |
| Flatpak | Flatpak | 1.11.1 (including) | 1.12.3 (including) |