CVE-2021-21261: Flatpak sandbox escape via spawn portal
First published: Thu Jan 14 2021(Updated: )
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. A bug was discovered in the `flatpak-portal` service that can allow sandboxed applications to execute arbitrary code on the host system (a sandbox escape). This sandbox-escape bug is present in versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. The Flatpak portal D-Bus service (`flatpak-portal`, also known by its D-Bus service name `org.freedesktop.portal.Flatpak`) allows apps in a Flatpak sandbox to launch their own subprocesses in a new sandbox instance, either with the same security settings as the caller or with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses that will process untrusted web content, and give those subprocesses a more restrictive sandbox than the browser itself. In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system, and in particular to the `flatpak run` command that is used to launch the new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the `flatpak run` command, and use them to execute arbitrary code that is not in a sandbox. As a workaround, this vulnerability can be mitigated by preventing the `flatpak-portal` service from starting, but that mitigation will prevent many Flatpak apps from working correctly. This is fixed in versions 1.8.5 and 1.10.0.
Credit: security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Flatpak Flatpak | >=0.11.4<1.8.5 | |
| Flatpak Flatpak | >=1.9.1<1.10.0 | |
| Debian Debian Linux | =10.0 | |
| debian/flatpak | 1.2.5-0+deb10u4 1.10.8-0+deb11u1 1.10.7-0+deb11u1 1.14.4-1 1.14.4-2 |
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Reference Links
- https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486
- https://github.com/flatpak/flatpak/commit/6e5ae7a109cdfa9735ea7ccbd8cb79f9e8d3ae8b
- https://github.com/flatpak/flatpak/commit/aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4
- https://github.com/flatpak/flatpak/commit/cc1401043c075268ecc652eac557ef8076b5eaba
- https://github.com/flatpak/flatpak/releases/tag/1.8.5
- https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
- https://security.gentoo.org/glsa/202101-21
- https://www.debian.org/security/2021/dsa-4830
- https://github.com/flatpak/flatpak/commit/821249844bbb7e52cbf4508b4de18c05e8592220
- https://github.com/flatpak/flatpak/commit/39a5621e6941b9d27bf89b63e8fb6cad6e279e53
- https://github.com/flatpak/flatpak/commit/d19f6c330aa42e17df6dc36d12b6f4dfa507dbb3
- https://www.openwall.com/lists/oss-security/2021/01/21/4
- https://security-tracker.debian.org/tracker/CVE-2021-21261
Frequently Asked Questions
What is CVE-2021-21261?
CVE-2021-21261 is a vulnerability in the flatpak-portal service that allows sandboxed applications to execute arbitrary code on the host system.
How does CVE-2021-21261 affect Linux systems?
CVE-2021-21261 affects Linux systems running the flatpak-portal service.
What is the severity of CVE-2021-21261?
CVE-2021-21261 has a severity rating of 8.8 (high).
Which versions of Flatpak are affected by CVE-2021-21261?
Flatpak versions 0.11.4 to 1.8.5 are affected by CVE-2021-21261.
How can I fix CVE-2021-21261?
To fix CVE-2021-21261, update Flatpak to version 1.2.5-0+deb10u4, 1.10.8-0+deb11u1, 1.10.7-0+deb11u1, 1.14.4-1, or 1.14.4-2.
- collector/nvd-index
- collector/security-tracker-debian
- agent/type
- agent/softwarecombine
- collector/mitre-cve
- source/MITRE
- agent/title
- agent/weakness
- agent/last-modified-date
- agent/author
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- vendor/flatpak
- canonical/flatpak flatpak
- version/flatpak flatpak/0.11.4
- version/flatpak flatpak/1.9.1
- vendor/debian
- canonical/debian debian linux
- version/debian debian linux/10.0
- package-manager/debian