A malicious SDK container can declare an extension point with a crafted directory path. When a developer runs flatpak build-init with the --writable-sdk and --sdk-extension flags, the path‑resolution function does not sanitize the input and allows .. traversal, enabling attacker‑chosen files to be written outside the working directory. This flaw permits arbitrary file writes in the host context.

The vulnerability affects Red Hat Enterprise Linux 10, 7, 8 and 9 systems that run Flatpak versions prior to 1.18.1.

The flaw is a path‑traversal weakness (CWE‑22). No EPSS score is available and it is not listed in CISA KEV. Exploitation requires the attacker to have the ability to run flatpak build‑init with the vulnerable SDK, a privilege typically held by developers or trusted build personnel. The risk is that arbitrary files can be written outside the intended workspace, potentially allowing unwanted modifications to host files. With a CVSS score of 9.8, the vulnerability is considered critical.