CVE-2026-63128

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.5%, top 56% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this week
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 7.5Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's stateful Streamable HTTP server in crates/rmcp/src/transport/streamable_http_server/tower.rs allows an unauthenticated client to send a well-formed JSON-RPC POST that is not an initialization request, or an initialization request with a mismatched protocol header, causing StreamableHttpService::handle_post to call LocalSessionManager.create_session before validating the message. An early validation failure returns without removing the inserted LocalSessionHandle from LocalSessionManager.sessions, permanently retaining session and channel state for the server process lifetime. Repeated requests can grow the shared session table without bound, degrade legitimate-client latency through lock contention, exhaust memory, and terminate the server. This issue is fixed in version 2.0.0.

CVSS v3
7.5
EG Score
7.5(medium)
EG Risk
38(Track)
EG Risk 38/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity75% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
44%
KEV
Not listed

Published

September 16, 2026

Last Modified

September 16, 2026

Advisory Details (4)

Auto-updated Sep 16, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_commit, github_pr, github_release.
github Patch Available🟡 PoC Available

Unauthenticated permanent session-table leak in rmcp Streamable HTTP server transport leads to remote denial-of-service · Advisory · modelcontextprotocol/rust-sdk · GitHub

Affected: 1.4.0 (

https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9pj6-vhgr-3mwh
github_release Patch Available

rmcp-v2.0.0

Patch available: modelcontextprotocol/rust-sdk rmcp-v2.0.0

https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0
github_pr Patch Available

fix: prevent streamable HTTP session leak

Patch available: modelcontextprotocol/rust-sdk rmcp-macros-v3.0.0-beta.1 (PR #934 merged 2026-06-27)

https://github.com/modelcontextprotocol/rust-sdk/pull/934
github_commit Patch Available

commit dfa7fd6f9309 (modelcontextprotocol/rust-sdk)

Patch available: modelcontextprotocol/rust-sdk rmcp-macros-v3.0.0-beta.1 (contains commit dfa7fd6f9309)

https://github.com/modelcontextprotocol/rust-sdk/commit/dfa7fd6f9309deab60bea230b041be9a3fcda846

Vendor Advisories for CVE-2026-63128(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
crates.io(1)
PackageVulnerable rangeFixed inDependents
rmcp—2.0.0—

Weakness Classification(3)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 6× in last 7d / 6× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-19 06:38 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-18 06:24 UTCEG score recompute
  4. 2026-09-16 15:20 UTCEG score recompute
  5. 2026-09-16 14:51 UTCEG score recompute
  6. 2026-09-16 14:50 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-63128?
CVE-2026-63128 is a high vulnerability published on September 16, 2026. RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's stateful Streamable HTTP server in crates/rmcp/src/transport/streamablehttpserver/tower.rs allows an unauthenticated client to send a well-formed JSON-RPC POST that is not an initialization request, or an…
When was CVE-2026-63128 disclosed?
CVE-2026-63128 was first published in the National Vulnerability Database on September 16, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-63128 actively exploited?
CVE-2026-63128 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 55.9% of all scored CVEs.
What is the CVSS score of CVE-2026-63128?
CVE-2026-63128 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-63128?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63128, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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