CVE-2026-39977
MediumCVSS 6.3Exploitation Probability (EPSS)
Low risk21th percentile - higher than 21% of all known CVEs
Summary
flatpak-builder from 1.4.5 to before 1.4.8 allows reading arbitrary host files via the license-files manifest key because path validation does not resolve symlinks in intermediate components. Copied files end up in the build output; the issue is fixed in 1.4.8.
Risk Assessment
A crafted manifest or source could leak sensitive host files into build artifacts, potentially exposing confidential data.
Recommendation
Update flatpak-builder to version 1.4.8 or later and avoid building untrusted manifests on hosts containing sensitive data.
Other vulnerabilities in flatpak-builder
See all- CVE-2026-107466Medium
A flaw was found in flatpak-builder. This vulnerability allows an attacker to cause information disclosure by convincing a user or continuous integration (CI) system to process a crafted build manifest. By specifying local file Uniform Resource Identifiers (URIs) within source download definitions, the builder bypasses directory confinement checks. As a result, sensitive host files accessible to the build process can be read and incorporated into the build artifacts.
- CVE-2026-86320High
A flaw was found in flatpak-builder where Git hooks are not disabled when applying patch sources with use-git-am: true. An attacker who can provide a malicious source containing a Git post-applypatch hook can cause the hook to execute on the host during the build process.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS