CVE-2026-64684

MEDIUMPre-NVD 6.86.8—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.8 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 67% 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
6.8EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.8Exploit: 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 2.1.0, the rmcp crate's StreamableHttpClientTransport in crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs builds its default_http_client with reqwest's automatic redirect policy and applies caller-supplied values from StreamableHttpClientTransportConfig.custom_headers without marking them as sensitive. When a malicious or compromised MCP endpoint returns a cross-origin 307 or 308 redirect, reqwest follows the redirect and apply_custom_headers causes custom API keys or authentication tokens to be replayed to the new origin, where an attacker can capture and reuse them. The separate auth_header path is not affected because it uses the standard Authorization header, which reqwest strips on cross-origin redirects. This issue is fixed in version 2.1.0.

CVSS v3
6.8
EG Score
6.8(medium)
EG Risk
31(Track)
EG Risk 31/100SSVC: 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
Severity68% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
33%
KEV
Not listed

Published

September 16, 2026

Last Modified

September 19, 2026

Advisory Details (4)

Auto-updated Sep 16, 2026
Patch available. Sources: github_commit, github_release, github, github_pr.
github_release Patch Available

rmcp-v2.1.0

Patch available: modelcontextprotocol/rust-sdk rmcp-v2.1.0

https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.1.0
github_commit Patch Available

commit 496902b9cf2c (modelcontextprotocol/rust-sdk)

Patch available: modelcontextprotocol/rust-sdk rmcp-macros-v3.0.0-beta.1 (contains commit 496902b9cf2c)

https://github.com/modelcontextprotocol/rust-sdk/commit/496902b9cf2c8a947454718da31829ae776b969b
github_pr Patch Available

fix: block redirect header leaks

Patch available: modelcontextprotocol/rust-sdk rmcp-macros-v3.0.0-beta.1 (PR #936 merged 2026-07-01)

https://github.com/modelcontextprotocol/rust-sdk/pull/936
github Patch Available

Custom HTTP headers leak to cross-origin redirect targets · Advisory · modelcontextprotocol/rust-sdk · GitHub

https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9g45-5xwm-f3wc

Vendor Advisories for CVE-2026-64684(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—2.1.0—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 8× in last 7d / 8× 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 02:28 UTCEG score recompute
  2. 2026-09-19 02:01 UTCEG score recompute
  3. 2026-09-18 22:49 UTCEG score recompute
  4. 2026-09-18 19:28 UTCEPSS rescore
  5. 2026-09-17 22:38 UTCEG score recompute
  6. 2026-09-16 22:26 UTCEG score recompute
  7. 2026-09-16 21:24 UTCEG score recompute
  8. 2026-09-16 21:24 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-64684?
CVE-2026-64684 is a medium vulnerability published on September 16, 2026. RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.1.0, the rmcp crate's StreamableHttpClientTransport in crates/rmcp/src/transport/common/reqwest/streamablehttpclient.rs builds its defaulthttpclient with reqwest's automatic redirect policy and applies caller-supplied values…
When was CVE-2026-64684 disclosed?
CVE-2026-64684 was first published in the National Vulnerability Database on September 16, 2026, with the most recent update on September 19, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-64684 actively exploited?
CVE-2026-64684 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 66.5% of all scored CVEs.
What is the CVSS score of CVE-2026-64684?
CVE-2026-64684 has a CVSS v3 base score of 6.8 (NVD).
How do I remediate CVE-2026-64684?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-64684, 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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