CVE-2026-100663

HIGHPre-NVD 7.57.5—
EchelonGraph scoreHIGH confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-09-26. A secondary CVSS source baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this weekElevated
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 7.5Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.2.Final through 4.2.17.Final does not special-case HTTP/1 CONNECT authority-form request-targets when converting HTTP/1 messages to HTTP/3 in HttpConversionUtil.toHttp3Headers. The authority-form target (e.g., "CONNECT trusted.example:443") is parsed as a URI, so its host is emitted as :scheme, :path is set to "/", and the HTTP/1 Host header is used as :authority; if no Host header is present the CONNECT target is dropped. In a Netty-based HTTP/1-to-HTTP/3 proxy or gateway, a remote client can send a CONNECT request whose Host header names a different authority than the request-target, producing a malformed HTTP/3 CONNECT whose tunnel :authority is attacker-controlled. This can bypass tunnel allow-lists, egress policy, backend selection, or audit controls that validate the HTTP/1 CONNECT request-target before forwarding over HTTP/3. The issue is fixed in 4.2.18.Final.

CVSS v3
7.5
EG Score
7.5HIGHhigh confidence
EG Risk
50
EG Risk 50/100CISA 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
Severity75% × 45%
Exploitation40% × 40%
Automatability0% × 15%
CISA SSVC: Track at low or medium mission impact; Track* at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
20th
KEV
Not listed

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

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

Exploitation public PoC (CISA Vulnrichment) · Automatable no (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 HTTP/1 CONNECT authority-form mistranslated to malformed HTTP/3 | Advisories | VulnCheck

https://www.vulncheck.com/advisories/netty-http-1-connect-authority-form-mistranslated-to-malformed-http-3
github Patch Available

HTTP/1 CONNECT target is mistranslated to malformed HTTP/3 CONNECT and Host-controlled :authority · Advisory · netty/netty · GitHub

https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627

Vendor Advisories for CVE-2026-100663(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 33× in last 7d / 39× 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 02:36 UTCGHSA enrichment
  2. 2026-10-03 15:08 UTCEG score recompute
  3. 2026-10-03 15:07 UTCGHSA enrichment
  4. 2026-10-03 14:25 UTCEPSS rescore
  5. 2026-10-03 03:32 UTCEG score recompute
  6. 2026-10-03 03:32 UTCGHSA enrichment
  7. 2026-10-02 16:02 UTCGHSA enrichment
  8. 2026-10-02 04:33 UTCEG score recompute
  9. 2026-10-02 04:33 UTCGHSA enrichment
  10. 2026-10-01 19:49 UTCEPSS rescore
  11. 2026-10-01 17:00 UTCGHSA enrichment
  12. 2026-10-01 05:01 UTCGHSA enrichment
  13. 2026-09-30 17:32 UTCEG score recompute
  14. 2026-09-30 17:32 UTCGHSA enrichment
  15. 2026-09-30 15:02 UTCEPSS rescore
  16. 2026-09-30 06:03 UTCGHSA enrichment
  17. 2026-09-29 18:34 UTCEG score recompute
  18. 2026-09-29 18:33 UTCGHSA enrichment
  19. 2026-09-29 15:20 UTCEPSS rescore
  20. 2026-09-29 06:58 UTCEG score recompute
  21. 2026-09-29 06:58 UTCGHSA enrichment
  22. 2026-09-28 19:29 UTCEG score recompute
  23. 2026-09-28 19:29 UTCGHSA enrichment
  24. 2026-09-28 18:52 UTCEG score recompute
  25. 2026-09-28 18:52 UTCGHSA enrichment
Show 14 more
  1. 2026-09-28 15:27 UTCEG score recompute
  2. 2026-09-28 15:27 UTCGHSA enrichment
  3. 2026-09-28 13:50 UTCEPSS rescore
  4. 2026-09-28 04:54 UTCGHSA enrichment
  5. 2026-09-27 17:24 UTCEG score recompute
  6. 2026-09-27 17:24 UTCGHSA enrichment
  7. 2026-09-27 16:35 UTCEG score recompute
  8. 2026-09-27 16:35 UTCGHSA enrichment
  9. 2026-09-27 13:32 UTCGHSA enrichment
  10. 2026-09-27 02:02 UTCEG score recompute
  11. 2026-09-27 02:02 UTCGHSA enrichment
  12. 2026-09-26 14:33 UTCEG score recompute
  13. 2026-09-26 13:37 UTCEG score recompute
  14. 2026-09-26 13:30 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-100663?
CVE-2026-100663 is a high vulnerability published on September 26, 2026. Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.2.Final through 4.2.17.Final does not special-case HTTP/1 CONNECT authority-form request-targets when converting HTTP/1 messages to HTTP/3 in HttpConversionUtil.toHttp3Headers. The authority-form target (e.g., "CONNECT trusted.example:443")…
When was CVE-2026-100663 disclosed?
CVE-2026-100663 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-2026-100663 actively exploited?
CVE-2026-100663 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (20th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-100663?
CVE-2026-100663 has a CVSS base score of 7.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-100663?
A fix for CVE-2026-100663 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-100663 are linked in the Vendor Advisories panel on this page.

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