CVE-2021-21261

NameCVE-2021-21261
DescriptionFlatpak 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.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, bugtraq, EDB, Metasploit, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, Mageia, GitHub code/issues, web search, more)
ReferencesDSA-4830-1
NVD severityhigh

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
flatpak (PTS)stretch0.8.9-0+deb9u3fixed
stretch (security)0.8.9-0+deb9u2fixed
buster, buster (security)1.2.5-0+deb10u4fixed
bullseye1.10.3-0+deb11u1fixed
bullseye (security)1.10.5-0+deb11u1fixed
bookworm, sid1.12.2-1fixed

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
flatpaksourcestretch(not affected)
flatpaksourcebuster1.2.5-0+deb10u2DSA-4830-1
flatpaksource(unstable)1.8.5-1

Notes

[stretch] - flatpak <not-affected> (app portal introduced in 0.11.4)
https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
Fixed by:
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
Automated tests:
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

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