Vulnerability · Published Nov 5, 2026 · Assigned by GitHub_M
CVE-2026-111771Model Context Protocol TypeScript SDK: Server bearer authentication accepted tokens issued for another service
Medium 6.8
In plain English
A medium-severity incorrect authorization in express from @modelcontextprotocol. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
The Model Context Protocol TypeScript SDK provides TypeScript client and server implementations of the Model Context Protocol. From 1.6.0 until 1.32.0 in @modelcontextprotocol/sdk, from 2.0.0 until 2.3.0 in @modelcontextprotocol/server, from 2.0.0 until 2.0.2 in @modelcontextprotocol/express, and from 2.0.0 until 2.3.1 in @modelcontextprotocol/server-legacy, server-side bearer authentication could accept a valid access token issued for a different service because the SDK did not enforce the token audience. The affected surface is server-side HTTP bearer authentication. The trigger is a valid token whose audience names another service. The authorization server must issue tokens for multiple services, and the application's verifyAccessToken() must not independently validate aud. Applications already validating aud inside verifyAccessToken() are not affected. An attacker with a token for another service could authenticate to the MCP server and obtain the confidentiality and integrity capabilities granted to an authenticated caller. Upgrading alone leaves the new audience validation disabled. Operators must enable audience validation and provide the token audience together. Enabling only the expected audience check causes every request to receive HTTP 401. This issue is fixed in @modelcontextprotocol/sdk 1.32.0, @modelcontextprotocol/server 2.3.0, @modelcontextprotocol/express 2.0.2, and @modelcontextprotocol/server-legacy 2.3.1.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | @modelcontextprotocol/express | 2.0.2 | GHSA-rvq5-wwqv-78pq |
| npm | @modelcontextprotocol/sdk | 1.32.0 | GHSA-rvq5-wwqv-78pq |
| npm | @modelcontextprotocol/server | 2.3.0 | GHSA-rvq5-wwqv-78pq |
| npm | @modelcontextprotocol/server-legacy | 2.3.1 | GHSA-rvq5-wwqv-78pq |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| modelcontextprotocol | typescript-sdk | >= 1.6.0, < 1.32.0 |
| @modelcontextprotocol | sdk | >= 1.6.0, < 1.32.0 |
| @modelcontextprotocol | server | >= 2.0.0, < 2.3.0 |
| @modelcontextprotocol | express | >= 2.0.0, < 2.0.2 |
| @modelcontextprotocol | server-legacy | >= 2.0.0, < 2.3.1 |
Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
References
- https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-rvq5-wwqv-78pq x_refsource_CONFIRM
- https://github.com/modelcontextprotocol/typescript-sdk/pull/2929 x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/pull/2930 x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/pull/2952 x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/commit/40f8f4e229d963cd7fd2890bda2aeebe7005299a x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/commit/5a0724d14cf34a27a3b070224d2996cdd611df9f x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/commit/5a1867390b91b8836f49af76c45427279f513325 x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/1.32.0 x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontextprotocol/express@2.0.2 x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontextprotocol/server-legacy@2.3.1 x_refsource_MISC
- https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/@modelcontextprotocol/server@2.3.0 x_refsource_MISC