CVE-2026-64684

MEDIUMPre-NVD 6.86.8
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

Score 6.8 from GitHub Security Advisory (severity: MODERATE) published 2026-09-17. A secondary CVSS source baseline 6.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source
Trending — 4 sources updated this week

Also known asEUVD-2026-81266 (ENISA EUVD) · GHSA-9g45-5xwm-f3wc (GitHub Security Advisories)Source: ENISA EUVD

6.8EG
EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.5%CVSS: 6.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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
6.8MEDIUMmedium confidence
EG Risk
31
EG Risk 31/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity68% × 45%
Impact severity (EG Severity): CVSS 6.8 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.5% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.5%
EPSS %ILE
42nd
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (6.8): severity, escalated by confirmed exploitation. This CVE's 6.8 is its impact severity (EG Severity), not escalated.

EG Severity
6.8 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.5% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-31). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

September 16, 2026

Last Modified

September 23, 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 pull request 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 advisoryMentions a patch (unverified)

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.

Patch Availability(1)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
rustrmcp @ 2.1.0 (fixes < 2.1.0)—ghsa

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
crates.io(1)
PackageVulnerable rangeFix by version rangeDependents
rmcp—
  • every version up to 2.1.0: fixed in 2.1.0
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 10× in last 7d / 48× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-11-02 16:45 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  2. 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  3. 2026-11-01 07:40 UTCEG score recompute
  4. 2026-11-01 07:40 UTCGHSA enrichmentGHSA-9g45-5xwm-f3wc · GitHub severity MODERATE · GitHub CVSS 6.8
  5. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  6. 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  7. 2026-10-30 08:25 UTCOSV refresh
  8. 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  9. 2026-10-28 16:32 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  10. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  11. 2026-10-26 16:32 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  12. 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  13. 2026-10-25 14:12 UTCEG score recompute
  14. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  15. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  16. 2026-10-22 19:42 UTCEG score recompute
  17. 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  18. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  19. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  20. 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  21. 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  22. 2026-10-18 03:22 UTCEG score recompute
  23. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  24. 2026-10-16 16:43 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  25. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.5% · 41st percentile
Show 52 more
  1. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  2. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  3. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  4. 2026-10-12 15:47 UTCEG score recompute
  5. 2026-10-11 19:32 UTCEG score recompute
  6. 2026-10-11 16:47 UTCEG score recompute
  7. 2026-10-11 14:08 UTCEG score recompute
  8. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  9. 2026-10-11 03:46 UTCEG score recompute
  10. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  11. 2026-10-10 02:48 UTCEG score recompute
  12. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  13. 2026-10-09 02:37 UTCEG score recompute
  14. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  15. 2026-10-08 02:27 UTCEG score recompute
  16. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  17. 2026-10-07 02:15 UTCEG score recompute
  18. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  19. 2026-10-06 02:04 UTCEG score recompute
  20. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  21. 2026-10-05 01:52 UTCEG score recompute
  22. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  23. 2026-10-04 01:41 UTCEG score recompute
  24. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  25. 2026-10-03 01:24 UTCEG score recompute
  26. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  27. 2026-10-02 01:10 UTCEG score recompute
  28. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  29. 2026-10-01 00:59 UTCEG score recompute
  30. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  31. 2026-09-30 00:48 UTCEG score recompute
  32. 2026-09-28 20:11 UTCEG score recompute
  33. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  34. 2026-09-27 19:46 UTCEG score recompute
  35. 2026-09-26 19:35 UTCEG score recompute
  36. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  37. 2026-09-24 18:39 UTCEG score recompute
  38. 2026-09-23 18:28 UTCEG score recompute
  39. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  40. 2026-09-23 03:13 UTCEG score recompute
  41. 2026-09-22 03:02 UTCEG score recompute
  42. 2026-09-21 02:50 UTCEG score recompute
  43. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  44. 2026-09-20 02:39 UTCEG score recompute
  45. 2026-09-19 02:28 UTCEG score recompute
  46. 2026-09-19 02:01 UTCEG score recompute
  47. 2026-09-18 22:49 UTCEG score recompute
  48. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  49. 2026-09-17 22:38 UTCEG score recompute
  50. 2026-09-16 22:26 UTCEG score recompute
  51. 2026-09-16 21:24 UTCEG score recomputeFirst assessed: 6.8 MEDIUM
  52. 2026-09-16 21:24 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-64684?
CVE-2026-64684 is a medium-severity vulnerability; its CVE record was 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/streamable_http_client.rs builds its default_http_client with reqwest's automatic redirect policy and applies caller-supplied…
When was the CVE record for CVE-2026-64684 published?
The CVE record for CVE-2026-64684 was published on September 16, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 23, 2026; the record at its source may have been updated since.
Is CVE-2026-64684 actively exploited?
CVE-2026-64684 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.5% probability of exploitation in the next 30 days (42nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-64684?
CVE-2026-64684 has a CVSS base score of 6.8 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-64684?
A fix for CVE-2026-64684 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-64684 are linked in the Vendor Advisories panel on this page.

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