Improper input validation in Flatpak
CVE-2021-41133
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. In versions prior to 1.10.4 and 1.12.0, Flatpak apps with direct access to AF_UNIX sockets such as those used by Wayland, Pipewire or pipewire-pulse can trick portals and other host-OS services into treating the Flatpak app as though it was an ordinary, non-sandboxed host-OS process. They can do this by manipulating the VFS using recent mount-related syscalls that are not blocked by Flatpak's denylist seccomp filter, in order to substitute a crafted `/.flatpak-info` or make that file disappear entirely. Flatpak apps that act as clients for AF_UNIX sockets such as those used by Wayland, Pipewire or pipewire-pulse can escalate the privileges that the corresponding services will believe the Flatpak app has. Note that protocols that operate entirely over the D-Bus session bus (user bus), system bus or accessibility bus are not affected by this. This is due to the use of a proxy process `xdg-dbus-proxy`, whose VFS cannot be manipulated by the Flatpak app, when interacting with these buses. Patches exist for versions 1.10.4 and 1.12.0, and as of time of publication, a patch for version 1.8.2 is being planned. There are no workarounds aside from upgrading to a patched version.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.004 (35.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 35.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
- Flatpak — versions >= 1.8.0, <= 1.8.2, >= 1.10.0, < 1.10.4, >= 1.11.0, < 1.12.0
- Debian Linux — versions 11.0
- Fedoraproject Fedora — versions 33, 34
Weakness classification (CWE)
Public proof-of-concept exploits
References
- github.com/flatpak/flatpak/security/advisories/GHSA-67h7-w3jq-vh4q (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/1330662f33a55e88bfe18e76de28b7922d91a999 (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/26b12484eb8a6219b9e7aa287b298a894b2f34ca (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/462fca2c666e0cd2b60d6d2593a7216a83047aaf (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/4c34815784e9ffda5733225c7d95824f96375e36 (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/89ae9fe74c6d445bb1b3a40e568d77cf5de47e48 (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/9766ee05b1425db397d2cf23afd24c7f6146a69f (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/a10f52a7565c549612c92b8e736a6698a53db330 (Patch, Third Party Advisory)
- github.com/flatpak/flatpak/commit/e26ac7586c392b5eb35ff4609fe232c52523b2cf (Patch, Third Party Advisory)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
Frequently asked questions
- What is CVE-2021-41133?
- CVE-2021-41133 is a high-severity vulnerability in Flatpak, classified under Improper Input Validation. CVSS score: 8.8/10. Published 2021-10-08.
- How severe is CVE-2021-41133?
- High severity. CVSS v3 base score is 8.8 out of 10.
- Is CVE-2021-41133 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.