CVE-2026-100659

MEDIUMPre-NVD 6.56.5—
EchelonGraph scoreHIGH confidence

Score 6.5 from GitHub Security Advisory published 2026-09-26. A secondary CVSS source baseline 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 6.5Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Netty's HTTP/3 codec (io.netty:netty-codec-http3) in versions 4.2.0.Final through 4.2.17.Final does not enforce the RFC 9114 requirement that the :authority pseudo-header field and a literal host header field, when both present, carry the same value. A remote unauthenticated peer can send a single HEADERS frame containing both fields with differing, attacker-controlled values; the request is accepted and delivered to the application with two conflicting authorities, allowing routing, virtual-host, and access-control decisions to be bypassed when different components in the request path consult different fields. This issue is fixed in 4.2.18.Final.

CVSS v3
6.5
EG Score
6.5MEDIUMhigh confidence
EG Risk
44
EG Risk 44/100CISA SSVC

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
Severity65% × 45%
Exploitation0% × 40%
Automatability100% × 15%
CISA SSVC: Track at low or medium mission impact; Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.2%
EPSS %ILE
13th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

September 26, 2026

Last Modified

September 28, 2026

Advisory Details (2)

Auto-updated Sep 26, 2026
Patch available. Sources: github.
generic

Netty 4.2.0 through 4.2.18 HTTP/3 Request Routing Bypass | Advisories | VulnCheck

https://www.vulncheck.com/advisories/netty-4.2.0-through-4.2.18-http-3-request-routing-bypass
github Patch Available

[codec-http3] Lack of Host header deduplication in HTTP/3 request handling leads to request routing bypass · Advisory · netty/netty · GitHub

https://github.com/netty/netty/security/advisories/GHSA-q9pg-8h3j-8hvm

Vendor Advisories for CVE-2026-100659(1)

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

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 27× in last 7d / 30× 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. 2026-10-04 03:57 UTCEG score recompute
  2. 2026-10-04 03:57 UTCGHSA enrichment
  3. 2026-10-03 14:25 UTCEPSS rescore
  4. 2026-10-03 02:55 UTCEG score recompute
  5. 2026-10-03 02:55 UTCGHSA enrichment
  6. 2026-10-02 01:52 UTCEG score recompute
  7. 2026-10-02 01:52 UTCGHSA enrichment
  8. 2026-10-01 19:49 UTCEPSS rescore
  9. 2026-10-01 00:49 UTCEG score recompute
  10. 2026-10-01 00:49 UTCGHSA enrichment
  11. 2026-09-30 15:02 UTCEPSS rescore
  12. 2026-09-29 23:48 UTCEG score recompute
  13. 2026-09-29 23:47 UTCGHSA enrichment
  14. 2026-09-29 15:20 UTCEPSS rescore
  15. 2026-09-28 19:30 UTCEG score recompute
  16. 2026-09-28 19:29 UTCGHSA enrichment
  17. 2026-09-28 18:37 UTCEG score recompute
  18. 2026-09-28 18:37 UTCGHSA enrichment
  19. 2026-09-28 15:27 UTCEG score recompute
  20. 2026-09-28 15:27 UTCGHSA enrichment
  21. 2026-09-28 13:50 UTCEPSS rescore
  22. 2026-09-27 17:24 UTCEG score recompute
  23. 2026-09-27 17:24 UTCGHSA enrichment
  24. 2026-09-27 16:36 UTCEG score recompute
  25. 2026-09-27 16:36 UTCGHSA enrichment
Show 5 more
  1. 2026-09-27 15:36 UTCEG score recompute
  2. 2026-09-27 15:36 UTCGHSA enrichment
  3. 2026-09-26 14:33 UTCEG score recompute
  4. 2026-09-26 13:37 UTCEG score recompute
  5. 2026-09-26 13:30 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-100659?
CVE-2026-100659 is a medium vulnerability published on September 26, 2026. Netty's HTTP/3 codec (io.netty:netty-codec-http3) in versions 4.2.0.Final through 4.2.17.Final does not enforce the RFC 9114 requirement that the :authority pseudo-header field and a literal host header field, when both present, carry the same value. A remote unauthenticated peer can send a single…
When was CVE-2026-100659 disclosed?
CVE-2026-100659 was first published on September 26, 2026, with the most recent update on September 28, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-100659 actively exploited?
CVE-2026-100659 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (13th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-100659?
CVE-2026-100659 has a CVSS base score of 6.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-100659?
A fix for CVE-2026-100659 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-100659 are linked in the Vendor Advisories panel on this page.

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