A flaw in act’s built‑in actions/cache server allows any entity that can reach the listening port to inject arbitrary cache entries. These entries can contain malicious files that, when a local action retrieves the cache, may be executed inside its Docker container, leading to unintended code execution on the host. The weakness is a missing authorization check when creating or retrieving caches.

The vulnerability affects the open‑source act tool from nektos. All releases prior to 0.2.86 are impacted; version 0.2.86 and later contain a fix that limits the cache server to specific interfaces or disables the feature by default.

The CVSS score of 8.2 indicates a high severity. EPSS data is not available, and the issue is not listed in the CISA KEV catalog. The likely attack vector is remote: an adversary that can reach the cache server over the network can create or read arbitrary cache entries. Successful exploitation would allow the attacker to run arbitrary code within the containers used by local GitHub Actions workflows, potentially affecting confidentiality, integrity, and availability of the host system.