Vulnerability in mcp (CVE-2026-59950)
Summary
Vulnerability in mcp (CVE-2026-59950). Confidential information can be exposed externally. Exploitable via mcp.server.websocket.websocket_server. Mitigation: upgrade to 1.28.1 or later.
Original description
The description as published by the source.
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.28.1, the deprecated mcp.server.websocket.websocket_server transport accepted WebSocket handshakes without applying Host or Origin header validation, leaving no SDK-level way to restrict which origins could connect to applications that exposed that transport. This issue is fixed in version 1.28.1.
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-2026-59950 has been found in mcp.
Attackers can target a specific entry point like mcp.server.websocket.websocket_server over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.1/10.
What to do: upgrade mcp to 1.28.1 or later.
If unsure, ask your IT team or search "mcp CVE-2026-59950" on the vendor's site.
CVE-2026-59950 (mcp) — CWE-346 / CVSS v3 8.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: mcp.server.websocket.websocket_server / Host / Origin / TransportSecuritySettings
Patched: 1.28.1 — 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.
A vulnerability (CWE-346) exists in mcp. Attackers reach the vulnerable code path via mcp.server.websocket.websocket_server without authentication.
Check the vendor advisory for the affected versions of mcp. Attack surface: mcp.server.websocket.websocket_server / Host / Origin / TransportSecuritySettings.
Severity: High (CVSS 8.1/10). Confidential information can be exposed externally.
Update to 1.28.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'mcp' . 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
-
1Identify exposure identify
grep -r 'mcp' . | 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
mcpを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade mcp to 1.28.1ステージング環境で 1.28.1 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。
-
3Post-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
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- advisory github.com
- package github.com
- package pypi.org
- patch github.com
- patch github.com
- web github.com