CVE-2026-103091: Insecure Default Policy and Unrestricted OIDC Enrollment in Google OSS Agent Mesh (SAM)

Severity: critical (CVSS 9.3 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-19 · updated 2026-10-19
Weakness: CWE-200

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.

Affected products

Google SAM: from 0.1.0-alpha.1 before 0.1.0-alpha.9 — fixed in 0.1.0-alpha.9

How to fix

Upgrade to a fixed version: Google SAM 0.1.0-alpha.9. Check the vendor advisory for mitigations.

References

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