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Response snapshot Oct 27, 2026, 07:01 UTC

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VulnerabilityCVE-2026-111771

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

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

At a glance

Exploited
Not known
Severity
6.8 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: @modelcontextprotocol/sdk: 1.32.0; @modelcontextprotocol/server: 2.3.0; @modelcontextprotocol/express: 2.0.2; @modelcontextprotocol/server-legacy: 2.3.1. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-rvq5-wwqv-78pq (opens a new tab)

What happened

### 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

Continue reading

### 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.

Affected package ranges reported by GitHub: @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

Scores and how they were measured

CVSS base severity

6.8

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-rvq5-wwqv-78pq (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-rvq5-wwqv-78pq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 20). MCP TypeScript SDK: Server bearer authentication accepted tokens issued for another service (CVE-2026-111771). https://kevwire.com/record/CVE-2026-111771

MLA

"MCP TypeScript SDK: Server bearer authentication accepted tokens issued for another service (CVE-2026-111771)." KEVWire, 20 Oct. 2026, kevwire.com/record/CVE-2026-111771.

Chicago

KEVWire. "MCP TypeScript SDK: Server bearer authentication accepted tokens issued for another service (CVE-2026-111771)." Last modified October 20, 2026. https://kevwire.com/record/CVE-2026-111771.

Evidence summary (plain text)

MCP TypeScript SDK: Server bearer authentication accepted tokens issued for another service (Oct 20, 2026).
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
CVSS 6.8 (version 3.1; evidence as of Oct 20, 2026; https://github.com/advisories/GHSA-rvq5-wwqv-78pq).
Sources:
GitHub-reviewed advisory GHSA-rvq5-wwqv-78pq: https://github.com/advisories/GHSA-rvq5-wwqv-78pq
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNTo1Mjo1NlrOAAfxiA%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNDowNjoxNFrOAAfxZw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQwODoyNzoyM1rOAAYp9A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozNTo1OFrOAAfwCQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozMDoxM1rOAAfv2A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyODowOVrOAAfv1g%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyNDoyMFrOAAfv1Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDo0NTowN1rOAAfvzQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDozMDoyNlrOAAfvxw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDowMzo1N1rOAAfvxQ%3D%3D
Record ID: CVE-2026-111771.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 20:55 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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