CVE-2026-100666

HIGHPre-NVD 7.37.3—
EchelonGraph scoreHIGH confidence

Score 7.3 from GitHub Security Advisory published 2026-09-26. A secondary CVSS source baseline 7.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this weekElevated
7.3EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 7.3Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

Netty's HttpServerCodec (io.netty:netty-codec-http) in versions 4.2.0.Final through 4.2.16.Final and in versions up to and including 4.1.136.Final pairs each outbound response with an inbound request by calling pollMethod() once per response, including for 1xx informational responses. If a client pipelines an HTTP/1.1 GET carrying an Expect: 100-continue header followed by a HEAD request, the 100 Continue response consumes the queued GET method, so the subsequent 200 OK for the GET is paired with HEAD and its body is dropped, while the following 200 OK for the HEAD request is written with a body. This desynchronizes HTTP parsing on the connection: the GET entity is never delivered and the HEAD response body is interpreted as the GET body, resulting in response splitting and unsafe connection reuse. Fixed in 4.2.17.Final and 4.1.137.Final.

CVSS v3
7.3
EG Score
7.3HIGHhigh confidence
EG Risk
64
EG Risk 64/100CISA 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
Severity73% × 45%
Exploitation40% × 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 public PoC (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 30, 2026

Advisory Details (2)

Auto-updated Sep 26, 2026
🔬 Proof of concept available. Patch available. Sources: github.
generic

Netty 4.2.0 through 4.2.17 Response Desynchronization via HttpServerCodec | Advisories | VulnCheck

https://www.vulncheck.com/advisories/netty-4.2.0-through-4.2.17-response-desynchronization-via-httpservercodec
github Patch Available🟡 PoC Available

HttpServerCodec response desynchronization · Advisory · netty/netty · GitHub

https://github.com/netty/netty/security/advisories/GHSA-2g6j-r8q9-5hr8

Vendor Advisories for CVE-2026-100666(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 34× in last 7d / 40× 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 08:04 UTCGHSA enrichment
  2. 2026-10-03 21:02 UTCEG score recompute
  3. 2026-10-03 21:02 UTCGHSA enrichment
  4. 2026-10-03 14:25 UTCEPSS rescore
  5. 2026-10-03 10:00 UTCGHSA enrichment
  6. 2026-10-02 22:58 UTCEG score recompute
  7. 2026-10-02 22:58 UTCGHSA enrichment
  8. 2026-10-02 11:55 UTCGHSA enrichment
  9. 2026-10-02 00:49 UTCEG score recompute
  10. 2026-10-02 00:49 UTCGHSA enrichment
  11. 2026-10-01 19:49 UTCEPSS rescore
  12. 2026-10-01 13:43 UTCGHSA enrichment
  13. 2026-10-01 02:41 UTCEG score recompute
  14. 2026-10-01 02:41 UTCGHSA enrichment
  15. 2026-09-30 15:39 UTCEG score recompute
  16. 2026-09-30 15:39 UTCGHSA enrichment
  17. 2026-09-30 15:02 UTCEPSS rescore
  18. 2026-09-30 15:02 UTCEG score recompute
  19. 2026-09-30 15:02 UTCGHSA enrichment
  20. 2026-09-30 11:36 UTCGHSA enrichment
  21. 2026-09-30 00:34 UTCEG score recompute
  22. 2026-09-30 00:34 UTCGHSA enrichment
  23. 2026-09-29 15:20 UTCEPSS rescore
  24. 2026-09-29 13:31 UTCGHSA enrichment
  25. 2026-09-29 02:29 UTCEG score recompute
Show 15 more
  1. 2026-09-29 02:29 UTCGHSA enrichment
  2. 2026-09-28 15:27 UTCEG score recompute
  3. 2026-09-28 15:27 UTCGHSA enrichment
  4. 2026-09-28 13:50 UTCEPSS rescore
  5. 2026-09-28 04:26 UTCGHSA enrichment
  6. 2026-09-27 17:24 UTCEG score recompute
  7. 2026-09-27 17:24 UTCGHSA enrichment
  8. 2026-09-27 16:35 UTCEG score recompute
  9. 2026-09-27 16:35 UTCGHSA enrichment
  10. 2026-09-27 12:40 UTCGHSA enrichment
  11. 2026-09-27 01:38 UTCEG score recompute
  12. 2026-09-27 01:37 UTCGHSA enrichment
  13. 2026-09-26 14:33 UTCEG score recompute
  14. 2026-09-26 13:37 UTCEG score recompute
  15. 2026-09-26 13:30 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-100666?
CVE-2026-100666 is a high vulnerability published on September 26, 2026. Netty's HttpServerCodec (io.netty:netty-codec-http) in versions 4.2.0.Final through 4.2.16.Final and in versions up to and including 4.1.136.Final pairs each outbound response with an inbound request by calling pollMethod() once per response, including for 1xx informational responses. If a client…
When was CVE-2026-100666 disclosed?
CVE-2026-100666 was first published on September 26, 2026, with the most recent update on September 30, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-100666 actively exploited?
CVE-2026-100666 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-2026-100666?
CVE-2026-100666 has a CVSS base score of 7.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-100666?
A fix for CVE-2026-100666 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-100666 are linked in the Vendor Advisories panel on this page.

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