CVE-2026-39977

Name	CVE-2026-39977
Description	flatpak-builder is a tool to build flatpaks from source. From 1.4.5 to before 1.4.8, the license-files manifest key takes an array of paths to user defined licence files relative to the source directory of the module. The paths from that array are resolved using g_file_resolve_relative_path() and validated to stay inside the source directory using two checks - g_file_get_relative_path() which does not resolve symlinks and g_file_query_file_type() with G_FILE_QUERY_INFO_NOFOLLOW_SYMLINKS which only applies to the final path component. The copy operation runs on host. This can be exploited by using a crafted manifest and/or source to read arbitrary files from the host and capture them into the build output. This vulnerability is fixed in 1.4.8.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1133099

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
flatpak-builder (PTS)	bullseye (security), bullseye	1.0.12-1+deb11u1	fixed
	bookworm	1.2.3-1	fixed
	trixie	1.4.4-2	fixed
	forky	1.4.7-1	vulnerable
	sid	1.4.8-1	fixed

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

Package	Type	Release	Fixed Version	Debian Bugs
flatpak-builder	source	bullseye	(not affected)
flatpak-builder	source	bookworm	(not affected)
flatpak-builder	source	trixie	(not affected)
flatpak-builder	source	(unstable)	1.4.8-1	1133099

Notes

[trixie] - flatpak-builder <not-affected> (Vulnerable code not present)
[bookworm] - flatpak-builder <not-affected> (Vulnerable code not present)
[bullseye] - flatpak-builder <not-affected> (Vulnerable code not present)
https://github.com/flatpak/flatpak-builder/security/advisories/GHSA-6gm9-3g7m-3965