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CVE-2026-63128 high CVSS 7.5

Vulnerability in rmcp (CVE-2026-63128)

Summary

Vulnerability in rmcp (CVE-2026-63128). Risk of unauthorized operations or information disclosure. Exploitable via LocalSessionManager. Mitigation: upgrade to 1.4.0 or later.

Original description

The description as published by the source.

Summary

An unauthenticated remote attacker can leak one entry per HTTP request out of the in-memory session table of LocalSessionManager by sending a well-formed JSON-RPC POST that is not an InitializeRequest. The Streamable HTTP server's handle_post allocates the session before it validates the body, then early-returns on the validation failure without calling close_session. The LocalSessionHandle (and the tokio mpsc channel internals it holds) is never released for the remainder of the process's lifetime — turning a ~250-byte request into a permanent ~400–550-byte server-side allocation that scales linearly with request volume and eventually exhausts memory. In the verified reproduction below, a single Python client sustains over 2 000 leak requests per second; that translates to roughly 170 million leaked entries per day, equivalent to ≈75 GB of resident memory just from the session table.

Details

The bug lives in crates/rmcp/src/transport/streamable_http_server/tower.rs inside StreamableHttpService::handle_post. The relevant slice of 1.7.0 source (lines 1126–1170) is:

} else {
    let (session_id, transport) = self
        .session_manager
        .create_session()                                                  // (★)
        .await
        .map_err(internal_error_response("create session"))?;
    // ...capture init params if a SessionStore is configured...
    if let ClientJsonRpcMessage::Request(req) = &mut message…

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-2026-63128 has been found in rmcp.
Attackers can target a specific entry point like LocalSessionManager over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade rmcp to 1.4.0 or later.
If unsure, ask your IT team or search "rmcp CVE-2026-63128" on the vendor's site.

CVE-2026-63128 (rmcp) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: LocalSessionManager / POST / InitializeRequest / handle_post
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-400) exists in rmcp. Attackers reach the vulnerable code path via LocalSessionManager without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of rmcp. Attack surface: LocalSessionManager / POST / InitializeRequest / handle_post.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 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 'rmcp' . 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 'rmcp' . | 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 rmcp 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 rmcp 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

rust rmcp
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.0"}]}]

References

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