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. 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.
Created flatpak tracking bugs for this issue: Affects: fedora-all [bug 1917431]
External References: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
Upstream fixes: https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486 https://github.com/flatpak/flatpak/commit/821249844bbb7e52cbf4508b4de18c05e8592220 https://github.com/flatpak/flatpak/commit/6e5ae7a109cdfa9735ea7ccbd8cb79f9e8d3ae8b https://github.com/flatpak/flatpak/commit/aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4 https://github.com/flatpak/flatpak/commit/39a5621e6941b9d27bf89b63e8fb6cad6e279e53 https://github.com/flatpak/flatpak/commit/cc1401043c075268ecc652eac557ef8076b5eaba https://github.com/flatpak/flatpak/commit/d19f6c330aa42e17df6dc36d12b6f4dfa507dbb3 Follow up commits (optional): https://github.com/flatpak/flatpak/commit/e2c4ded323161f47609d0af97d00019d04a635f1 https://github.com/flatpak/flatpak/commit/b0aea9c0533f8338ead9acb8dd2a65e6339b9a99 https://github.com/flatpak/flatpak/commit/4108e022452303093d8b90c838695a0476cb09c7 https://github.com/flatpak/flatpak/commit/c4a58d5822e86f82bbf9e2e7702153a51cc6841b
Mitigation: This vulnerability can be mitigated by preventing the flatpak-portal service from starting. Please note that this mitigation may prevent other Flatpak apps from working correctly.
Note from upstream advisory (comment 3): The initial fixes introduced a regression (#4080) for users of a setuid version of bubblewrap (bwrap). This is fixed in 1.10.1 (commits 9a61d2c [1] and fb473ca [2], also backported to the flatpak-1.8.x branch). [1] https://github.com/flatpak/flatpak/commit/9a61d2c44f0a58cebcb9b2787ae88db07ca68bb0 [2] https://github.com/flatpak/flatpak/commit/fb473cad801c6b61706353256cab32330557374a
Acknowledgments: Name: Simon McVittie (Collabora Ltd.)
This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2021:0304 https://access.redhat.com/errata/RHSA-2021:0304
This issue has been addressed in the following products: Red Hat Enterprise Linux 8.1 Extended Update Support Via RHSA-2021:0306 https://access.redhat.com/errata/RHSA-2021:0306
This issue has been addressed in the following products: Red Hat Enterprise Linux 8.2 Extended Update Support Via RHSA-2021:0307 https://access.redhat.com/errata/RHSA-2021:0307
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2021-21261
This issue has been addressed in the following products: Red Hat Enterprise Linux 7 Via RHSA-2021:0411 https://access.redhat.com/errata/RHSA-2021:0411