EUVD-2026-21045
CVSS 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
3Description
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.
Analysis
Path traversal in flatpak-builder 1.4.5 through 1.4.7 enables arbitrary host file exfiltration through license-files manifest exploitation. Attacker-crafted manifest with symlink manipulation bypasses g_file_get_relative_path() and g_file_query_file_type() validation, allowing reads outside source directory. …
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Remediation
Within 24 hours: Inventory all systems running flatpak-builder 1.4.5-1.4.7 and restrict manifest processing to trusted internal sources only; prohibit processing manifests from untrusted external repositories. Within 7 days: Implement application-level controls (e.g., file system sandboxing, SELinux policies limiting flatpak-builder directory access) and audit recent builds for suspicious manifest usage. …
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External POC / Exploit Code
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