Woodpecker CI gRPC Vulnerability Allows Cross-Tenant Agent Impersonation (CVE-2026-50141)

A significant security flaw, tracked as CVE-2026-50141, was discovered in the gRPC communication layer of Woodpecker CI, a continuous integration platform. This vulnerability enabled any authenticated Woodpecker agent to effectively impersonate another agent residing on the same server. The core issue stemmed from the server's handling of agent_id metadata within gRPC requests. While the server correctly validated the JSON Web Token (JWT) provided by the client, it erroneously prioritized a client-supplied agent_id value over the verified identity derived from the JWT. This design flaw meant that a malicious or compromised agent could forge its identity, bypassing security controls and gaining unauthorized access to resources or executing actions typically reserved for the impersonated agent. The vulnerability impacts Woodpecker CI v3 versions, specifically from 3.0.0 up to, but not including, 3.14.1. This could lead to severe consequences for organizations using affected versions, including unauthorized code execution, data exfiltration, or disruption of CI/CD pipelines.

Attack Chain

1. An attacker gains authenticated access as any legitimate, potentially low-privileged, Woodpecker agent to the CI server.
2. The attacker crafts a gRPC request, intending to perform an action or access resources.
3. Within the gRPC request metadata, the attacker injects a forged agent_id value corresponding to a target agent they wish to impersonate.
4. The malicious gRPC request is sent to the Woodpecker CI server.
5. The server receives the request and correctly verifies the JWT token, confirming the attacker's original, legitimate agent identity.
6. During subsequent processing, the server incorrectly discards the verified agent identity from the JWT.
7. The server then prioritizes and accepts the forged agent_id supplied in the gRPC metadata by the attacker.
8. The server executes the requested action or grants access to resources as if the request originated from the impersonated target agent, leading to unauthorized operations or privilege escalation.

Impact

Successful exploitation of CVE-2026-50141 allows an attacker to achieve cross-tenant agent impersonation within a Woodpecker CI environment. This can lead to significant unauthorized access and control over CI/CD pipelines, potentially enabling malicious actors to trigger builds, deploy unauthorized code, access sensitive repositories, or exfiltrate intellectual property. Organizations using affected versions of Woodpecker CI (v3.0.0 through v3.14.0) are at risk of severe operational disruption and data breaches. While no specific victim count or targeted sector is provided, any organization leveraging Woodpecker CI for their development workflows is a potential target.

Recommendation

• Patch CVE-2026-50141 immediately: Upgrade Woodpecker CI v3 to version 3.14.1 or later to apply the necessary security patches mentioned in the references.
• Implement workarounds if patching is not immediate: As a temporary mitigation, disable organization agents by setting WOODPECKER_DISABLE_USER_AGENT_REGISTRATION=true and delete any existing organization agents.
• Review logs for unusual gRPC activity: While specific detection rules are challenging for this vulnerability, monitor Woodpecker CI server logs for any anomalies in agent behavior or unexpected actions attributed to specific agents, particularly after an agent has been authenticated.