MCP TypeScript SDK: Server bearer authentication accepted tokens issued for another service

### Summary In affected versions, the SDK's server-side bearer authentication had no way to check that a token was issued for your server (its audience). Where one authorization server issues tokens for several services, a valid token for another service was also accepted by your MCP server. ### Am I affected? Yes, if your HTTP server uses `requireBearerAuth()` or `verifyBearerToken()`, its authorization server also issues tokens for other services, and your `verifyAccessToken()` does not check the token's audience (`aud`) itself. Affected versions: - `@modelcontextprotocol/sdk` 1.6.0 through 1.31.0 - `@modelcontextprotocol/server` 2.0.0 through 2.2.0 - `@modelcontextprotocol/express` 2.0.0 through 2.0.1 - `@modelcontextprotocol/server-legacy` 2.0.0 through 2.3.0 ### Fix Upgrade to: - 1.x: `@modelcontextprotocol/sdk` 1.32.0 or later - 2.x: `@modelcontextprotocol/server` 2.3.0 or later, together with `@modelcontextprotocol/express` 2.0.2 or later if you use it - `@modelcontextprotocol/server-legacy` 2.3.1 or later **Upgrading alone changes nothing.** The patched versions add an `expectedResource` setting that is off by default. To turn the check on, make both of these changes together: 1. Pass the audience your authorization server puts in tokens for your server: `requireBearerAuth({ verifier, expectedResource: new URL('https://mcp.example.com/mcp') })`. 2. Return the token's audience from `verifyAccessToken()` as `AuthInfo.resource`, also a `URL`. A token for another service then gets `401`. With only the first change, every request gets `401`. If you cannot upgrade yet, reject any token whose `aud` does not include your server inside `verifyAccessToken()`. That closes the issue on every version.

CVSS 3.1

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

Severity from

GitHub (reviewed advisory)

Weakness

CWE-863

Also known as

CVE-2026-111771

• github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-rvq5-wwqv-78pq
• github.com/modelcontextprotocol/typescript-sdk/commit/40f8f4e229d963cd7fd2890bda2aeebe7005299a
• github.com/modelcontextprotocol/typescript-sdk/commit/5a0724d14cf34a27a3b070224d2996cdd611df9f
• github.com/modelcontextprotocol/typescript-sdk/commit/5a1867390b91b8836f49af76c45427279f513325
• github.com/modelcontextprotocol/typescript-sdk