The vulnerability arises because Flatpak accepts an "arch" parameter without validation, allowing a crafted value to traverse the intended root directory when the flatpak-system-helper process creates directories based on an OCI remote definition. The result is a root‑owned directory tree and associated files, enabling a local attacker to gain elevated privileges if combined with another vulnerability fixed in the same release. This path traversal flaw is classified as CWE‑22. The impact is that a malicious local user with an active session can create directories outside the allowed sandbox, potentially leading to local root privilege escalation.

This issue exists in all Flatpak releases prior to 1.18.1 on Linux systems that have at least one OCI remote configured, which is common on Fedora distributions. Flatpak processes the OCI remote metadata when flatpak-system-helper runs, so any configured remote makes the vulnerability exploitable. Flatpak 1.18.1 and later contain the patch that prevents unvalidated path traversal.

With a CVSS score of 7.2 the vulnerability is considered high. The EPSS score is not published, and the vulnerability is not yet listed in CISA KEV, which suggests there is no widespread exploitation yet. Attackers must be local users with an active session and must have at least one OCI remote configured. The attack does not involve network interaction, but the existence of multiple pre‑existing local privileges could be required to combine with other fixes. Because of the local nature, the risk is significant for systems where Fedora‑style OCI remote configuration is used.