CVE-2021-21381

high

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`.

References

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/[email protected]/message/2MXXLXC2DPJ45HSMTI5MZYHMYEGQN6AA/

https://lists.fedoraproject.org/archives/list/[email protected]/message/WXNVFOIB6ZP4DGOVKAM25T6OIEP3YLGV/

https://www.debian.org/security/2021/dsa-4868

Details

Source: MITRE

Published: 2021-03-11

Updated: 2021-03-25

Type: CWE-74

Risk Information

CVSS v2

Base Score: 5.8

Vector: AV:N/AC:M/Au:N/C:P/I:P/A:N

Impact Score: 4.9

Exploitability Score: 8.6

Severity: MEDIUM

CVSS v3

Base Score: 8.2

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Impact Score: 5.8

Exploitability Score: 1.8

Severity: HIGH