Vulnerability · Published Mar 11, 2021 · Assigned by GitHub_M
CVE-2021-21381Sandbox escape via special tokens in .desktop file
High 7.1
In plain English
A high-severity injection in flatpak from flatpak. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.5% (higher than 75% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. In Flatpack since version 0.9.4 and before version 1.10.2 has a vulnerability in the "file forwarding" feature which can be used by an attacker to gain access to files that would not ordinarily be allowed by the app's permissions. By putting the special tokens `@@` and/or `@@u` in the Exec field of a Flatpak app's .desktop file, a malicious app publisher can trick flatpak into behaving as though the user had chosen to open a target file with their Flatpak app, which automatically makes that file available to the Flatpak app. This is fixed in version 1.10.2. A minimal solution is the first commit "`Disallow @@ and @@U usage in desktop files`". The follow-up commits "`dir: Reserve the whole @@ prefix`" and "`dir: Refuse to export .desktop files with suspicious uses of @@ tokens`" are recommended, but not strictly required. As a workaround, avoid installing Flatpak apps from untrusted sources, or check the contents of the exported `.desktop` files in `exports/share/applications/*.desktop` (typically `~/.local/share/flatpak/exports/share/applications/*.desktop` and `/var/lib/flatpak/exports/share/applications/*.desktop`) to make sure that literal filenames do not follow `@@` or `@@u`.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | flatpak | 1.10.1-4 | DEBIAN-CVE-2021-21381 |
| Debian:13 | flatpak | 1.10.1-4 | DEBIAN-CVE-2021-21381 |
| Debian:14 | flatpak | 1.10.1-4 | DEBIAN-CVE-2021-21381 |
Affected products (as reported)
Weakness: CWE-74 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N
References
- https://github.com/flatpak/flatpak/security/advisories/GHSA-xgh4-387p-hqpp
- https://github.com/flatpak/flatpak/pull/4156
- https://github.com/flatpak/flatpak/commit/8279c5818425b6812523e3805bbe242fb6a5d961
- https://github.com/flatpak/flatpak/commit/a7401e638bf0c03102039e216ab1081922f140ae
- https://github.com/flatpak/flatpak/commit/eb7946bb6248923d8c90fe9b84425fef97ae580d
- https://github.com/flatpak/flatpak/releases/tag/1.10.2
- DSA-4868 vendor-advisory
- FEDORA-2021-26ad138ffa vendor-advisory
- FEDORA-2021-fe7decc595 vendor-advisory
- GLSA-202312-12 vendor-advisory