The vulnerability resides in Fission’s SanitizeFilePath function, which relies on a simple lexical HasPrefix check to ensure a path stays within a safe directory. Because the check does not enforce a path-separator boundary, a sibling directory whose name begins with the safe-directory string can be used to bypass the intended restriction. This flaw allows a tenant that can create or control such a sibling directory to read or write files outside the intended safe directory, potentially compromising application data or executing unintended code within the tenant’s workspace.

Fission users running any version prior to 1.25.0 are affected. The issue appears in the builder’s Clean handler and the fetcher’s Fetch/Upload handlers, which are part of the Fission open‑source, Kubernetes‑native serverless framework. Version 1.25.0 and later include the patch that corrects the directory boundary check.

The CVSS score of 3.6 indicates low overall severity, and the EPSS score is not available; the vulnerability is not listed in the CISA KEV catalog. However, the attack vector is likely exercised by a tenant with access to the builder or fetcher endpoints—an inferred scenario because the flaw hinges on tenant ability to pre‑create a sibling directory under the shared volume. The potential impact is read/write beyond the intended safe directory, which could lead to data leakage or code execution within the tenant’s environment. The risk is therefore low to moderate, but mitigation remains recommended.