Missing Authorization (CWE-862) and Initialization of a Resource with an Insecure Default…

Why it is Amber

• CVSS 9.3 critical
• Remotely exploitable without logging in

References

• https://github.com/google/sam/releases/tag/v0.1.0-alpha.9
• https://github.com/google/sam/security/advisories/GHSA-cgmg-9xf6-rrgw
• https://github.com/google/agentmesh/security/advisories/GHSA-cgmg-9xf6-rrgw

Original description

Missing Authorization (CWE-862) and Initialization of a Resource with an Insecure Default (CWE-1188) in the MCP proxy (HandleStreamPassThrough in mcp_service.go) and OIDC registration flow (GET /info and POST /register in internal/controlplane/server.go) in Google OSS Agent Mesh (SAM) versions 0.1.0-alpha.1 through 0.1.0-alpha.8 allow a remote attacker to self-enroll into the mesh and invoke arbitrary tools across all connected MCP backend nodes. Because GET /info publicly discloses OIDC configuration, POST /register auto-enrolls any valid OIDC token holder without claim filtering or ban checks, and the default policy binds sam:system:authenticated to wildcard services and targets, an attacker can obtain a mesh credential with full read, write, and execution access on backend services. Users should upgrade to version 0.1.0-alpha.9 or later, which enforces a fail-closed default policy, explicit policy-binding requirements on enrollment, and ban checks.