CVE-2026-89139
HighCVSS 8.7Summary
Temporal Server vulnerability allows an authenticated user with write access to a single namespace to execute arbitrary commands on the host running the Worker Service. The command is executed immediately, and since the Worker Service process holds credentials and TLS material for the entire cluster, the impact escalates to full cluster compromise. Affected versions are 1.31.0 through 1.31.2 (before 1.31.3), and the issue is present in default binaries and container images.
Risk Assessment
An attacker can take over the Worker Service and thus the entire Temporal cluster, as the process has access to sensitive credentials for all namespaces. This could lead to full system and data compromise.
Recommendation
It is recommended to immediately upgrade Temporal Server to version 1.31.3 or later if you are running 1.31.0–1.31.2. Additionally, if an upgrade is not possible, configure the compute provider allowlist (workercontroller.compute_providers.enabled) to exclude the "subprocess" provider and ensure the value is explicitly set.
Other vulnerabilities in Temporal Server
See all- CVE-2026-87858High
Temporal Server in releases 1.30.0 and later decided whether a Workflow completion callback was internal by reading a caller-supplied HTTP header. An authenticated caller with write permission in a single namespace could attach a callback whose 'source' header caused the request to be re-targeted at the internal frontend and executed as a system administrator against the administrative API. Releases 1.25.0 through 1.29.7 are affected by a narrower form of the same defect requiring the header to match a configured cluster ID.
- CVE-2026-16652High
Temporal Server did not bound the work performed while searching for a Schedule's next action time. An authenticated caller with namespace write permission could create or update a Schedule combining a fine-grained cadence with an exclusion calendar that rejects every candidate time, causing excessive CPU consumption in Frontend and Schedule worker components.
- CVE-2026-5724Medium
The frontend gRPC server's streaming interceptor chain did not include the authorization interceptor. Configured ClaimMapper and Authorizer were bypassed for the AdminService/StreamWorkflowReplicationMessages endpoint, allowing unauthenticated access.
- CVE-2023-3485Low
Insecure defaults in open-source Temporal Server before version 1.20 on all platforms allow an attacker to craft a task token with access to a namespace other than the one specified in the request. This requires the namespace UUID and information from the workflow history for the target namespace.
Original NVD description (English source)
Temporal Server compiles a Worker Controller Instance module into its Worker Service, and that module registers a compute provider named subprocess whose function is to launch a worker by running a command on the machine hosting the Worker Service. The program name and the argument vector that provider executes are taken from the compute provider configuration supplied in the caller's request rather than from operator configuration. An authenticated caller holding only a write role in a single namespace can therefore configure a worker deployment version so that the Worker Service executes a command of the caller's choosing on its own host, under the account the server process runs as. Execution is immediate rather than deferred: the configuration handler invokes every provider using the invoke strategy directly after validating the submitted specification, so no scaling decision, task arrival, or unusual request sequence is required. Because the Worker Service process holds the persistence credentials for every namespace in the cluster and the cluster's TLS material, the consequence reaches beyond the caller's namespace to the cluster as a whole. The provider is present in the official temporal-server binaries and container images for the affected releases. The only control that can keep it unreachable is the compute provider allowlist, the per-namespace dynamic configuration setting workercontroller.compute_providers.enabled, and that control does not deny by default: its default value is an unset list, and the allowlist check is skipped entirely when the value is unset, so every registered compute provider is permitted, this one included. To determine whether a deployment is affected, check the following together. The deployed Temporal Server version is 1.31.0 or later and earlier than 1.31.3. The Worker Service is running, which it is in the default service set and therefore in a stock deployment. The effective per-namespace value of workercontroller.compute_providers.enabled is either unset or contains subprocess. And authorization is configured, meaning a real authorizer and claim mapper are in place; a deployment running with no authorizer already grants every caller unrestricted access to every namespace, so it has no namespace boundary for this to cross. Note that the separate per-namespace dynamic configuration setting workercontroller.enabled does not gate the affected path. It defaults to false, and a deployment that has never set it in any namespace is still affected, which was confirmed by running an affected release with no value for that setting present anywhere in dynamic configuration. To look for a compute configuration that is already attached, call DescribeWorkerDeploymentVersion for each worker deployment version in each namespace and check whether any scaling group's compute provider type is subprocess.