Sign in Sign up
JA · EN · FR
SecPulse
Categories
CVE-2026-104850 high CVSS 7.5

Vulnerability in @modelcontextprotocol/sdk (CVE-2026-104850)

Summary

Vulnerability in @modelcontextprotocol/sdk (CVE-2026-104850). Confidential information can be exposed externally. Exploitable via refresh_token. Mitigation: upgrade to 1.31.0 or later.

Original description

The description as published by the source.

Summary

In affected versions, the SDK's OAuth client let the MCP server decide which authorization server received the client's OAuth credentials. Credentials were not tied to the authorization server they belong to.

A malicious or compromised MCP server could name its own authorization server. With no user interaction, the client would send it:

  • the refresh_token and client_secret stored from an earlier sign-in
  • the client_secret or signed assertion configured on a bundled provider

Am I affected?

Yes, if both of these hold:

  • your application uses the SDK's OAuth client over HTTP, through any of:
    • an authProvider on a transport
    • the withOAuth() middleware
    • direct calls to auth() or fetchToken()
  • it may connect to an MCP server you do not fully trust while holding credentials for a legitimate authorization server

Affected versions:

  • @modelcontextprotocol/sdk 1.12.0 through 1.30.1
  • @modelcontextprotocol/client 2.0.0 through 2.1.0, only for:
    • bundled providers without expectedIssuer
    • credentials stored or supplied without issuer
    • direct calls to fetchToken()
    • providers that read storage back through OAuthTokensSchema or OAuthClientInformationSchema

Not affected:

  • MCP servers built with the SDK
  • stdio clients

Fix

Upgrade to:

  • 1.x: @modelcontextprotocol/sdk 1.31.0 or later
  • 2.x: @modelcontextprotocol/client 2.2.0 or later, and @modelcontextprotocol/core 2.2.0 or later if you import…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-104850 has been found in @modelcontextprotocol/sdk.
Attackers can target a specific entry point like refresh_token over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.5/10.
What to do: upgrade @modelcontextprotocol/sdk to 1.31.0 or later.
If unsure, ask your IT team or search "@modelcontextprotocol/sdk CVE-2026-104850" on the vendor's site.

CVE-2026-104850 (@modelcontextprotocol/sdk) — CWE-345 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: refresh_token / client_secret / authProvider / expectedIssuer
Patched: 1.31.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-345) exists in @modelcontextprotocol/sdk. Attackers reach the vulnerable code path via refresh_token without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of @modelcontextprotocol/sdk. Attack surface: refresh_token / client_secret / authProvider / expectedIssuer.

🔥 Severity

Severity: High (CVSS 7.5/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 1.31.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@modelcontextprotocol/sdk' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r '@modelcontextprotocol/sdk' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で @modelcontextprotocol/sdk を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade @modelcontextprotocol/sdk to 1.31.0

    ステージング環境で 1.31.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm @modelcontextprotocol/sdk
[{"type":"SEMVER","events":[{"introduced":"1.12.0"},{"fixed":"1.31.0"}]}]
npm @modelcontextprotocol/client
[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"2.2.0"}]}]

References

We use cookies for analytics and ad measurement. This setting applies to all Game co., Ltd. sites. Details