# MCP accepts a token for another resource

A protected MCP resource accepts a token that was not issued for that resource.

**Candidate CWE:** [CWE-287](https://cwe.mitre.org/data/definitions/287.html)

## Test hypothesis

Use local issuer fixtures to compare a correctly issued token with an otherwise valid token intended only for a second owned resource. Request the same harmless protected operation with each.

## Evidence required

Expected resource, redacted issuer/audience/scope claims, verification outcome and unauthorized synthetic response.

## Rule out false positives

Some deployments intentionally define a valid audience set; compare against actual issuer and resource policy, not a guessed hostname.

## Playbook and command references

- [AI tools: input trust, execution identity and approvals](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/modules/ai-tool-trust.html) — Prove when lower-trust content changes a protected tool action, then locate the missing authorization or consent boundary.
- [Authentication, recovery, federation, and session lifecycle](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/modules/identity-session.html) — Test registration, recovery, identity changes, invitations, SSO enforcement, and deprovisioning as one account state machine.

[Find the associated command snippets](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/commands.html?q=AI%20tools%3A%20input%20trust%2C%20execution%20identity%20and%20approvals)

## Referenced by these target playbooks

[AI, agents & MCP](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/ai.html) · [Web & API](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/web-api.html) · [OSS & self-hosted](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/oss.html)

## Report checklist

- [ ] Capture the affected version, configuration, identities, and object ownership.
- [ ] Preserve a valid baseline and a negative control.
- [ ] Reproduce the forbidden data access, action, or state change on controlled fixtures.
- [ ] Explain the intended security rule and why the observed behavior violates it.
- [ ] State prerequisites, uncertainty, cleanup, and the smallest demonstrated impact.

## Conditional ATT&CK mapping

- [T1550.001 · Use Alternate Authentication Material: Application Access Token](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/attack.html#T1550-001) — **Only if:** A captured or improperly obtainable application token is actually accepted for access to a protected service or resource outside the actor's intended permissions. **Not established by:** Finding a token alone is not reuse; routine authorized API calls are not this behavior. Current Enterprise tactic metadata lists Lateral Movement, not the old Defense Evasion label.

## Primary references

- [MCP Authorization 2026-07-28](https://modelcontextprotocol.io/specification/2026-07-28/basic/authorization)

[Back to the complete vulnerability catalog](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/vulnerabilities.html)