CVE-2026-39977
6.3 · MEDIUMOverview
CVE-2026-39977 is a medium-severity vulnerability affecting flatpak flatpak-builder. It was published on April 9, 2026 and has a CVSS 3.1 base score of 6.3 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 6.3, rated MEDIUM. It requires local or adjacent network access to exploit. No authentication or special privileges are required for exploitation.
Technical 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.
Remediation
Check the references section for vendor advisories and patches from flatpak. Update flatpak-builder to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| flatpak | flatpak-builder | >= 1.4.5, < 1.4.8 | Affected |
Frequently Asked Questions
What is CVE-2026-39977?
CVE-2026-39977 is a medium-severity vulnerability affecting flatpak flatpak-builder. It was published on April 9, 2026 and has a CVSS 3.1 base score of 6.3 (MEDIUM).
How severe is CVE-2026-39977?
This vulnerability has a CVSS 3.1 base score of 6.3, rated MEDIUM. It requires local or adjacent network access to exploit. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-39977?
Check the references section for vendor advisories and patches from flatpak. Update flatpak-builder to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-39977?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-39977 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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