Vulnerability in mcp/sdk (CVE-2026-53965)
Summary
Vulnerability in mcp/sdk (CVE-2026-53965). Risk of unauthorized operations or information disclosure. Exploitable via memory_limit. Mitigation: upgrade to 0.7.1 or later.
Original description
The description as published by the source.
Summary
The HTTP client transport in mcp/sdk reads a Server-Sent-Events (SSE) response
stream incrementally and appends each 4 KiB chunk to an in-memory buffer
($this->sseBuffer .= $chunk;) with no upper bound. The buffer is only ever
flushed when an SSE event delimiter ("\n\n") appears. A remote MCP server (the
peer the client connects to) that streams response bytes without ever sending the
"\n\n" delimiter makes $sseBuffer grow without limit until the client process
exhausts its PHP memory_limit (fatal "Allowed memory size … exhausted") or is
killed by the OS OOM-killer.
This is a denial-of-service against the MCP client: any server it talks to —
or a network position that controls the server's response body — can crash the
client by withholding the event delimiter while streaming data.
Impact
- Type: Denial of service (memory exhaustion / process crash) of the MCP client.
- Who can trigger it: The remote MCP server endpoint the client connects to via
HttpTransport, or any party that can control/inject into that server's SSE
response body (e.g. a man-in-the-middle on a plaintext endpoint, or a malicious
or compromised server). The buffer growth happens while the transport is reading
the response stream, before a complete event is ever parsed. - Effect: A response stream of N bytes containing no
"\n\n"drives the client's
resident buffer to track N. A few hundred MB of delimiter-free data is enough to
kill a client r…
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-2026-53965 has been found in mcp/sdk.
Attackers can target a specific entry point like memory_limit over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade mcp/sdk to 0.7.1 or later.
If unsure, ask your IT team or search "mcp/sdk CVE-2026-53965" on the vendor's site.
CVE-2026-53965 (mcp/sdk) — CWE-400
Attack surface: memory_limit / HttpTransport / strpos / poc_sse.php
Patched: 0.7.1 — 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-400) exists in mcp/sdk. Attackers reach the vulnerable code path via memory_limit.
Check the vendor advisory for the affected versions of mcp/sdk. Attack surface: memory_limit / HttpTransport / strpos / poc_sse.php.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 0.7.1.
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/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
-
1Identify exposure identify
grep -r 'mcp/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
mcp/sdk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/sdk to 0.7.1ステージング環境で 0.7.1 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
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web security-advisories@github.com