CVE-2021-21381: Sandbox escape via special tokens in .desktop file
First published: Thu Mar 11 2021(Updated: )
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`.
Credit: security-advisories@github.com security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| >=0.9.4<1.10.2 | ||
| =10.0 | ||
| =33 | ||
| =34 | ||
| Flatpak Flatpak | >=0.9.4<1.10.2 | |
| Debian Debian Linux | =10.0 | |
| Fedoraproject Fedora | =33 | |
| Fedoraproject Fedora | =34 | |
| debian/flatpak | 1.2.5-0+deb10u4 1.10.8-0+deb11u1 1.10.7-0+deb11u1 1.14.4-1 1.14.5-1 |
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Reference Links
- 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/pull/4156
- https://github.com/flatpak/flatpak/releases/tag/1.10.2
- https://github.com/flatpak/flatpak/security/advisories/GHSA-xgh4-387p-hqpp
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/2MXXLXC2DPJ45HSMTI5MZYHMYEGQN6AA/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WXNVFOIB6ZP4DGOVKAM25T6OIEP3YLGV/
- https://www.debian.org/security/2021/dsa-4868
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WXNVFOIB6ZP4DGOVKAM25T6OIEP3YLGV/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2MXXLXC2DPJ45HSMTI5MZYHMYEGQN6AA/
- https://security.gentoo.org/glsa/202312-12
- https://github.com/flatpak/flatpak/issues/4146
- https://security-tracker.debian.org/tracker/CVE-2021-21381
Frequently Asked Questions
What is CVE-2021-21381?
CVE-2021-21381 is a vulnerability in Flatpak, a system for building, distributing, and running sandboxed desktop applications on Linux.
What is the severity of CVE-2021-21381?
The severity of CVE-2021-21381 is high with a CVSS score of 8.2.
How does CVE-2021-21381 affect Flatpak?
CVE-2021-21381 affects Flatpak versions 0.9.4 to 1.10.2, allowing an attacker to gain access to files that would not ordinarily be accessible.
Which operating systems are affected by CVE-2021-21381?
CVE-2021-21381 affects Debian Linux 10.0, Fedora 33, and Fedora 34.
How do I fix CVE-2021-21381?
To fix CVE-2021-21381, upgrade Flatpak to version 1.2.5-0+deb10u4 or higher for Debian, version 1.10.8-0+deb11u1 or higher for Debian 11, or version 1.14.4-1 or higher for Fedora.
- collector/nvd-index
- collector/security-tracker-debian
- agent/references
- agent/type
- agent/last-modified-date
- agent/remedy
- agent/first-publish-date
- agent/author
- agent/softwarecombine
- agent/weakness
- agent/title
- agent/severity
- agent/description
- agent/event
- collector/nvd-api
- source/NVD
- agent/software-canonical-lookup
- agent/tags
- collector/mitre-cve
- source/MITRE
- vendor/flatpak
- canonical/flatpak flatpak
- version/flatpak flatpak/0.9.4
- vendor/debian
- canonical/debian debian linux
- version/debian debian linux/10.0
- vendor/fedoraproject
- canonical/fedoraproject fedora
- version/fedoraproject fedora/33
- version/fedoraproject fedora/34
- package-manager/debian