flatpak-builder EUVD-2026-94800

Exploitation requires that flatpak-builder process an attacker-controlled build manifest (JSON/YAML module definition) that specifies a local file:// URI inside a source download definition; the flaw is the bypass of flatpak-builder's directory confinement checks for such local sources. Realistic preconditions and limits: the victim developer or CI system must actually run a build against the untrusted manifest (UI:R), the targeted files must be readable by the user running the build, and the practical high-value target is CI/CD pipelines that auto-build community-submitted manifests. It is not remotely exploitable without someone initiating a build, which materially constrains opportunistic exploitation.

This is a moderate-severity information disclosure flaw (CVSS 6.1) that is best treated as medium priority rather than an urgent fix. The provided CVSS vector (AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N) is internally consistent with the description: the attack is local in the sense that a malicious build manifest must be processed on the target host, requires no pre-existing privileges (PR:N), but hinges on user or CI interaction (UI:R) to run flatpak-builder against the attacker-supplied manifest. The high confidentiality impact (C:H) is justified because arbitrary host files readable by the build process can be exfiltrated into build artifacts. No EPSS score, KEV listing, or POC was provided; per available data there is no public exploit identified at time of analysis, so there is no evidence of active or at-scale exploitation. The key limiting factor is social-engineering/supply-chain dependency - the victim must be convinced to build an untrusted manifest - which keeps real-world risk below what the C:H impact alone might suggest. The most relevant exposure is CI/CD pipelines that automatically build third-party or community-submitted manifests, where 'user interaction' is effectively automated and secrets on the build host may be harvested.

An attacker submits or publishes a crafted flatpak build manifest that references a local-file URI (e.g. file:///etc or a path to CI secrets) in a source download definition. A developer or an automated CI system processes the manifest with flatpak-builder, which fails to enforce directory confinement and reads the sensitive host file, embedding its contents into the resulting build artifact for the attacker to retrieve. No public exploit code was identified in the provided data.