CVE-2026-39977 flatpak-builder has a path traversal leading to arbitrary file read on host when installing licence files
Attackers can read arbitrary host files during Flatpak builds via crafted manifests, exposing sensitive data to build outputs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-39977?
CVE-2026-39977 is a high-severity path traversal vulnerability in flatpak-builder, published on 9 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-22
Which versions are affected by CVE-2026-39977?
It affects 1 product.
Linux distribution packages (1)
flatpak-builder openSUSE:Tumbleweed | All versions | 1.4.8-1.1 |
Products include Flatpak Flatpak-Builder.
How do I fix CVE-2026-39977?
Upgrade to a fixed version.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-39977 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39977 exists.
Sources
Also known as DEBIAN-CVE-2026-39977, GHSA-6gm9-3g7m-3965, UBUNTU-CVE-2026-39977, openSUSE-SU-2026:10590-1.