CVE-2026-42559

HIGHNVD 8.88.8—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.8 under NVD CVSS v3. EPSS exploit probability: 0.2%, top 88% 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, nvd
Trending — 3 sources updated this week
8.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 8.8Exploit: NoneExposed: 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 version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.

CVSS v3
8.8
EG Score
8.8(medium)
EG Risk
40(Track)
EG Risk 40/100SSVC: 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
Severity88% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
11.7%
KEV
Not listed

Published

May 14, 2026

Last Modified

May 14, 2026

Advisory Details (5)

Auto-updated May 14, 2026
Patch available. Sources: github.
github Patch Available

DNS rebinding vulnerability in rmcp Streamable HTTP server transport · Advisory · modelcontextprotocol/rust-sdk · GitHub

https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx
generic

fix(http): add host check by jokemanfire · Pull Request #764 · modelcontextprotocol/rust-sdk · GitHub

https://github.com/modelcontextprotocol/rust-sdk/pull/764
generic

Add Origin header validation for defense-in-depth in Streamable HTTP server · Issue #822 · modelcontextprotocol/rust-sdk · GitHub

https://github.com/modelcontextprotocol/rust-sdk/issues/822
generic

[SECURITY] Status of DNS Rebinding Vulnerability Fix for rust-sdk · Issue #815 · modelcontextprotocol/rust-sdk · GitHub

https://github.com/modelcontextprotocol/rust-sdk/issues/815
generic

fix(http): add host check (#764) · modelcontextprotocol/rust-sdk@8e22aa2 · GitHub

https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3

Vendor Advisories for CVE-2026-42559(1)

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

Affected Packages

(3 across 2 ecosystems)
crates.io(2)
PackageVulnerable rangeFixed inDependents
dynoxide-rs—0.9.13—
rmcp—1.4.0—
npm(1)
PackageVulnerable rangeFixed inDependents
dynoxide—0.9.13—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 9× in last 7d / 34× 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. 2026-07-23 03:11 UTCEG score recompute
  2. 2026-07-22 14:08 UTCEPSS rescore
  3. 2026-07-21 15:24 UTCEPSS rescore
  4. 2026-07-20 17:08 UTCEPSS rescore
  5. 2026-07-19 14:31 UTCEPSS rescore
  6. 2026-07-19 02:29 UTCEPSS rescore
  7. 2026-07-18 10:04 UTCEPSS rescore
  8. 2026-07-18 01:59 UTCOSV refresh
  9. 2026-07-16 17:03 UTCEPSS rescore
  10. 2026-07-15 16:57 UTCEPSS rescore
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  1. 2026-06-30 23:22 UTCEPSS rescore
  2. 2026-06-29 14:06 UTCEPSS rescore
  3. 2026-06-28 14:07 UTCEPSS rescore
  4. 2026-06-28 04:56 UTCEPSS rescore
  5. 2026-06-27 03:08 UTCEPSS rescore
  6. 2026-06-25 13:49 UTCEPSS rescore
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  8. 2026-06-24 14:05 UTCEPSS rescore
  9. 2026-06-23 21:33 UTCEPSS rescore
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  14. 2026-06-21 01:59 UTCEPSS rescore
  15. 2026-06-19 19:25 UTCEPSS rescore
  16. 2026-06-18 17:52 UTCEPSS rescore
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  18. 2026-06-17 17:53 UTCEPSS rescore
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  20. 2026-06-15 17:49 UTCEPSS rescore
  21. 2026-06-12 23:12 UTCEPSS rescore
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  23. 2026-06-10 22:18 UTCEPSS rescore
  24. 2026-06-10 13:22 UTCEPSS rescore
  25. 2026-06-10 13:22 UTCEPSS rescore
  26. 2026-06-08 14:17 UTCEPSS rescore
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  28. 2026-06-07 15:25 UTCEPSS rescore
  29. 2026-06-07 15:25 UTCEPSS rescore
  30. 2026-06-06 13:47 UTCEPSS rescore
  31. 2026-06-06 13:47 UTCEPSS rescore
  32. 2026-06-05 06:10 UTCEPSS rescore
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  34. 2026-06-04 13:12 UTCEPSS rescore
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  36. 2026-06-02 20:13 UTCEPSS rescore
  37. 2026-06-01 13:52 UTCEPSS rescore
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  39. 2026-05-31 22:30 UTCEPSS rescore
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  41. 2026-05-31 00:16 UTCEPSS rescore
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  43. 2026-05-29 13:44 UTCEPSS rescore
  44. 2026-05-29 13:44 UTCEPSS rescore
  45. 2026-05-27 13:40 UTCEPSS rescore
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  47. 2026-05-26 13:44 UTCEPSS rescore
  48. 2026-05-26 07:18 UTCEPSS rescore
  49. 2026-05-26 07:18 UTCEPSS rescore
  50. 2026-05-20 22:38 UTCEPSS rescore
  51. 2026-05-20 22:38 UTCEPSS rescore
  52. 2026-05-20 12:17 UTCEG score recompute
  53. 2026-05-20 11:22 UTCEPSS rescore
  54. 2026-05-20 11:22 UTCEPSS rescore

Frequently asked(5)

What is CVE-2026-42559?
CVE-2026-42559 is a high vulnerability published on May 14, 2026. RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamablehttpserver/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to…
When was CVE-2026-42559 disclosed?
CVE-2026-42559 was first published in the National Vulnerability Database on May 14, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-42559 actively exploited?
CVE-2026-42559 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 11.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-42559?
CVE-2026-42559 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2026-42559?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-42559, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-42559

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