CVE-2026-5724: Temporal Server Auth Bypass Vulnerability

CVE-2026-5724 Overview

CVE-2026-5724 is an authorization bypass vulnerability in the Temporal workflow orchestration platform. The frontend gRPC server's streaming interceptor chain fails to include the authorization interceptor, allowing unauthenticated access to the AdminService/StreamWorkflowReplicationMessages endpoint. While unary RPCs properly enforce authentication and authorization when a ClaimMapper and Authorizer are configured, this streaming endpoint accepts requests without credentials.

Critical Impact

An attacker with network access to the frontend port can open the replication stream without authentication, potentially leading to data exfiltration when specific cluster configuration conditions are met.

Affected Products

• Temporal Server versions prior to v1.28.4
• Temporal Server versions prior to v1.29.6
• Temporal Server versions prior to v1.30.4

Discovery Timeline

• April 10, 2026 - CVE-2026-5724 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5724

Vulnerability Analysis

This vulnerability is classified under CWE-306 (Missing Authentication for Critical Function). The core issue lies in an inconsistent security architecture where the gRPC interceptor chain applies different authentication rules to unary versus streaming RPC calls. When administrators configure ClaimMapper and Authorizer components to secure their Temporal deployment, they reasonably expect all endpoints to be protected. However, the streaming AdminService/StreamWorkflowReplicationMessages endpoint operates outside this security model.

The attack surface is amplified because this vulnerable endpoint is registered on the same port as the WorkflowService and cannot be disabled independently. Organizations cannot simply close the endpoint without impacting legitimate workflow functionality, leaving them exposed until they can apply patches.

Root Cause

The root cause is an architectural oversight in the interceptor chain configuration. When building the gRPC server, the authorization interceptor was properly added to the unary RPC handler chain but was inadvertently omitted from the streaming interceptor chain. This creates a gap where streaming endpoints bypass the authentication and authorization checks that protect other API calls.

Attack Vector

An attacker with network access to the Temporal frontend port can exploit this vulnerability by directly calling the AdminService/StreamWorkflowReplicationMessages streaming endpoint without providing any authentication credentials. The attack follows this sequence:

1. The attacker identifies a Temporal deployment with the frontend port exposed
2. They establish a gRPC connection to the frontend service
3. Without authenticating, they invoke the StreamWorkflowReplicationMessages streaming RPC
4. The server accepts the connection because the streaming interceptor chain lacks authorization checks

While data exfiltration is possible, exploitation is limited by several conditions: a replication target must be correctly configured, and the attacker must have knowledge of the cluster configuration. The history service validates cluster IDs and peer membership before returning replication data, which provides some defense in depth. Temporal Cloud deployments are not affected by this vulnerability.

Detection Methods for CVE-2026-5724

Indicators of Compromise

• Unexpected connections to the AdminService/StreamWorkflowReplicationMessages endpoint from unknown IP addresses
• gRPC stream requests to the frontend port lacking authentication headers or credentials
• Anomalous replication stream activity outside of configured replication windows
• Connection attempts from hosts not part of the expected cluster peer membership

Detection Strategies

• Enable gRPC access logging and monitor for calls to AdminService/StreamWorkflowReplicationMessages without corresponding authentication events
• Implement network-level monitoring for unauthorized connections to the Temporal frontend port
• Review audit logs for replication stream requests that bypass the configured ClaimMapper/Authorizer

Monitoring Recommendations

• Deploy network segmentation to limit access to Temporal frontend ports to authorized hosts only
• Configure alerts for any gRPC streaming connections that do not follow normal authentication patterns
• Monitor cluster membership and replication target configurations for unauthorized modifications

How to Mitigate CVE-2026-5724

Immediate Actions Required

• Upgrade Temporal Server to patched versions: v1.28.4, v1.29.6, or v1.30.4 depending on your current version branch
• Implement network-level access controls to restrict access to the frontend gRPC port to trusted hosts only
• Review existing network configurations to ensure the Temporal frontend is not unnecessarily exposed to untrusted networks
• Audit logs for any suspicious access to the StreamWorkflowReplicationMessages endpoint prior to patching

Patch Information

Temporal has released security patches that address this authorization bypass. The patches add the authorization interceptor to the streaming interceptor chain, ensuring consistent authentication enforcement across all RPC types.

Workarounds

• Restrict network access to the Temporal frontend port using firewall rules or network security groups
• Deploy Temporal behind a network load balancer or API gateway that can enforce authentication at the network edge
• If using Kubernetes, implement NetworkPolicies to limit pod-to-pod communication with the Temporal frontend

# Example: Restrict access to Temporal frontend port using iptables
# Allow only trusted cluster members to access port 7233
iptables -A INPUT -p tcp --dport 7233 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 7233 -j DROP