Temporal Server includes a Worker Controller Instance module that registers a compute provider named subprocess. The subprocess provider launches a worker by executing a program and argument vector supplied directly from the caller’s request, rather than from operator configuration. An authenticated caller with a write role in a single namespace can therefore instruct the Worker Service to run any command it chooses on the server host, under the account the Temporal Server process runs as. The command executes immediately during the configuration handling phase, so no scaling trigger or special request sequence is required. Because the Worker Service holds persistence credentials for every namespace and the cluster’s TLS material, this privilege extends beyond the attacker’s namespace and can jeopardize cluster‑wide secrets and services.

The flaw affects Temporal Server versions 1.31.0, 1.31.1, and 1.31.2 when deployed with the default workercontroller.compute_providers.enabled setting unset or containing subprocess. The 1.30 release line is unaffected, and the 1.32.0 and 1.31.3 releases include a patch that changes the compute provider allowlist to deny‑by‑default. The vulnerability is present only when the per‑namespace dynamic configuration setting workercontroller.compute_providers.enabled is unset, empty, or includes subprocess and when an authorizer is present, allowing the caller to gain write access to a namespace.

The CVSS score of 8.7 indicates high severity. EPSS is not available, but the attack is straightforward: a client must be authenticated with a write role in a namespace, which many deployments grant to developers. The exploit can be carried out with a single API request and does not require any unusual network traffic or scaling events. Although the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog, the combination of high impact, easy exploitation path, and cluster‑wide consequences warrants urgent attention.