What’s Vulnerable › Vulnerabilities
CVE-2026-39977: flatpak-builder has a path traversal leading to arbitrary file read on host when installing licence files
- Severity: medium (CVSS 6.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.3% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-04-09 · updated 2026-10-26
- Weakness: CWE-22
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.
Affected products
- flatpak-builder: from 1.4.5 before 1.4.8 — fixed in 1.4.8
How to fix
Upgrade to a fixed version: flatpak-builder 1.4.8. Check the vendor advisory for mitigations.
References
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