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

> Remote attackers can self-enroll into the mesh and execute arbitrary tools on backend nodes due to insecure default policies and unrestricted OIDC registration.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-cgmg-9xf6-rrgw, GHSA-qx8v-pq9p-7g7v

## What is CVE-2026-103091?

CVE-2026-103091 is a critical missing authorization vulnerability in Google SAM, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-862 (Missing Authorization), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), CWE-863 (Incorrect Authorization), CWE-306 (Missing Authentication for Critical Functionality), CWE-1188 (Initialization of a Resource with an Insecure Default)

## Which versions are affected by CVE-2026-103091?


## How do I fix CVE-2026-103091?

No fix has been published for CVE-2026-103091 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103091 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-103091 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103091 and fix it if it is affected.

What it is: CVE-2026-103091 is a critical missing authorization vulnerability in Google SAM, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-103091 exists.

Affected product: Google SAM. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-103091/ (Markdown: https://insights.sbomify.com/CVE-2026-103091/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103091
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103091
- OSV: https://osv.dev/vulnerability/CVE-2026-103091

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103091/
Summaries are generated and may contain mistakes; the official description above is the record.