Vulnerability in mcp (CVE-2026-67432)
Summary
Vulnerability in mcp (CVE-2026-67432). Risk of unauthorized operations or information disclosure. Exploitable via String. Mitigation: upgrade to 0.23.0 or later.
Original description
The description as published by the source.
Summary
An unauthenticated remote attacker can force any MCP Ruby SDK server using MCP::Server::Transports::StreamableHTTPTransport to allocate gigabytes of memory by sending a single oversized JSON-RPC POST. The transport reads the entire HTTP body into a Ruby String and parses it with JSON.parse(body, symbolize_names: true) with no size limit, no Content-Length pre-check, and no streaming parser, allowing trivial denial of service against the worker process.
Affected component
lib/mcp/server/transports/streamable_http_transport.rb, method handle_post:
- Line 341:
body_string = request.body.read— reads the full HTTP body into memory with no upper bound. - Lines 531–535:
JSON.parse(body_string, symbolize_names: true)— fully materialises the parsed object graph; withsymbolize_names: trueevery JSON key also allocates a Ruby symbol.
The vulnerable path runs before session validation, so it is reachable in both the default stateful mode and in stateless: true mode, without an Mcp-Session-Id header and without any prior authentication.
A second instance of the same root cause exists in lib/mcp/server/transports/stdio_transport.rb:23 ($stdin.gets with no limit: argument). The practical impact there is limited because the stdio peer is normally a trusted parent process, but the fix should cover both transports.
Proof of concept
Both files below are self-contained. Save them anywhere on disk, run the server in one terminal and the…
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-2026-67432 has been found in mcp.
Attackers can target a specific entry point like String over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade mcp to 0.23.0 or later.
If unsure, ask your IT team or search "mcp CVE-2026-67432" on the vendor's site.
CVE-2026-67432 (mcp) — CWE-770 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: String / handle_post / oom_poc_server.rb / oom_poc_client.py
Patched: 0.23.0 — 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.
A vulnerability (CWE-770) exists in mcp. Attackers reach the vulnerable code path via String without authentication.
Check the vendor advisory for the affected versions of mcp. Attack surface: String / handle_post / oom_poc_server.rb / oom_poc_client.py.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 0.23.0.
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 0.23.0ステージング環境で 0.23.0 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。
-
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 nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com