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CVE-2026-34742 high CVSS 8.1

Vulnerability in github.com/modelcontextprotocol/go-sdk (CVE-2026-34742)

Summary

Vulnerability in github.com/modelcontextprotocol/go-sdk (CVE-2026-34742). Confidential information can be exposed externally. Exploitable via StreamableHTTPHandler. Mitigation: upgrade to 1.4.0 or later.

Original description

The description as published by the source.

The Model Context Protocol (MCP) Go SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication with StreamableHTTPHandler or SSEHandler, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances.

Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport.

Servers created via StreamableHTTPHandler or SSEHandler now have this protection enabled by default when binding to localhost. Users are advised to update to version 1.4.0 to receive this automatic protection.

Source: NIST National Vulnerability Database 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-2026-34742 has been found in github.com/modelcontextprotocol/go-sdk.
Attackers can target a specific entry point like StreamableHTTPHandler over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.1/10.
What to do: upgrade github.com/modelcontextprotocol/go-sdk to 1.4.0 or later.
If unsure, ask your IT team or search "github.com/modelcontextprotocol/go-sdk CVE-2026-34742" on the vendor's site.

CVE-2026-34742 (github.com/modelcontextprotocol/go-sdk) — CWE-1188 / CVSS v3 8.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: StreamableHTTPHandler / SSEHandler / localhost
Patched: 1.4.0 — 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-1188) exists in github.com/modelcontextprotocol/go-sdk. Attackers reach the vulnerable code path via StreamableHTTPHandler without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/modelcontextprotocol/go-sdk. Attack surface: StreamableHTTPHandler / SSEHandler / localhost.

🔥 Severity

Severity: High (CVSS 8.1/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 1.4.0.

🛡️ 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 'github.com/modelcontextprotocol/go-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 'github.com/modelcontextprotocol/go-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 github.com/modelcontextprotocol/go-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 github.com/modelcontextprotocol/go-sdk to 1.4.0

    ステージング環境で 1.4.0 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

go github.com/modelcontextprotocol/go-sdk
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.4.0"}]}]

References

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