The vulnerability lies in BuildKit’s cache mount source= selector when operating on Windows Container on Windows (WCOW) workers. It fails to detect NTFS directory junctions that exist inside the cache root, allowing a build authored by an untrusted user to cause the BuildKit daemon process to resolve these junctions to locations outside the intended cache directory. As a result, the build can read arbitrary host files that are reachable to the BuildKit daemon process, exposing potentially sensitive data such as credentials, configuration files, or other secrets. The flaw is a classic example of an “Unrestricted File Disclosure”.

The affected product is moby:BuildKit, specifically any BuildKit deployment configured to run WCOW workers. No specific version information is provided in the advisory; the issue applies to any BuildKit installation where the cache mount source= selector is used on Windows hosts.

The CVSS score of 5.6 indicates moderate severity, and the EPSS score is < 1%, indicating a very low probability of exploitation. The vulnerability is not listed in CISA’s KEV catalog. Based on the description, the attack vector is inferred to be local or untrusted build submission: an attacker who can influence the build source or provide build daemon to read unintended host files. No privilege escalation or remote code execution is described; the primary risk is the disclosure of host files.