CVE-2026-100666

HIGHPre-NVD 7.37.3
EchelonGraph scoreMEDIUM confidence

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

Score 7.3 from GitHub Security Advisory (severity: MODERATE) published 2026-09-26. A secondary CVSS source baseline 7.3; 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 weekElevated

Also known asEUVD-2026-87760 (ENISA EUVD) · GHSA-jq5g-c66v-g3r2 (GitHub Security Advisories)Source: ENISA EUVD

7.3EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 7.3Exploit: No code on recordExposed 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
7.3HIGHmedium confidence
EG Risk
64
EG Risk 64/100

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)
Severity73% × 45%
Impact severity (EG Severity): CVSS 7.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation public PoC (CISA Vulnrichment) · Automatable yes (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 at low or medium mission impact and sooner than that at high.
EPSS PROB
0.3%
EPSS %ILE
22nd
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 (7.3): severity, escalated by confirmed exploitation. This CVE's 7.3 is its impact severity (EG Severity), not escalated.

EG Severity
7.3 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). 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 low or medium mission impact; Attend at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; 60 days 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 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). 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)14 days if the affected system is publicly exposed; 60 days if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable yes (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 26, 2026

Last Modified

September 30, 2026

Advisory Details (2)

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

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 advisoryMentions a patch (unverified)

HttpServerCodec response desynchronization · Advisory · netty/netty · GitHub

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

Patch Availability(2)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatdevspaces/server-rhel9:17927756392026-10-26redhat
redhatnetty-codec-http2026-10-15redhat

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

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
netty1:4.1.48-10 ... 1:4.1.48-9 (12 versions)
  • every version on: no fix on record
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
netty1:4.1.48-10 ... 1:4.1.48-16 (8 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
netty1:4.1.48-10 ... 1:4.1.48-16 (7 versions)
  • every version on: no fix on record
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 13× in last 7d / 74× 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.

Showing the most recent 100 of 110 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 10 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-02 01:58 UTCEG score recompute
  2. 2026-11-02 01:58 UTCVendor advisory
  3. 2026-11-02 01:58 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub severity MODERATE · GitHub CVSS 7.3
  4. 2026-11-01 16:33 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
  5. 2026-10-31 16:31 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
  6. 2026-10-30 16:33 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
  7. 2026-10-29 16:32 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  8. 2026-10-28 16:31 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  9. 2026-10-27 16:31 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  10. 2026-10-26 16:30 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  11. 2026-10-26 15:32 UTCEG score recompute
  12. 2026-10-26 15:32 UTCVendor advisory
  13. 2026-10-26 15:32 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  14. 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  15. 2026-10-25 15:58 UTCEG score recompute
  16. 2026-10-24 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  17. 2026-10-24 06:41 UTCEG score recompute
  18. 2026-10-24 06:41 UTCVendor advisory
  19. 2026-10-24 06:40 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  20. 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  21. 2026-10-22 16:33 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  22. 2026-10-21 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  23. 2026-10-20 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  24. 2026-10-19 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  25. 2026-10-18 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
Show 75 more
  1. 2026-10-18 05:11 UTCEG score recompute
  2. 2026-10-17 20:11 UTCEG score recompute
  3. 2026-10-17 20:11 UTCVendor advisory
  4. 2026-10-17 20:11 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  5. 2026-10-17 16:33 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  6. 2026-10-16 16:40 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  7. 2026-10-15 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  8. 2026-10-14 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  9. 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  10. 2026-10-12 16:41 UTCEG score recompute
  11. 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  12. 2026-10-11 19:55 UTCEG score recompute
  13. 2026-10-11 19:55 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  14. 2026-10-11 18:29 UTCEG score recompute
  15. 2026-10-11 15:02 UTCEG score recompute
  16. 2026-10-11 13:47 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  17. 2026-10-11 08:53 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  18. 2026-10-10 21:50 UTCEG score recompute
  19. 2026-10-10 21:50 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  20. 2026-10-10 19:59 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  21. 2026-10-10 10:22 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  22. 2026-10-09 23:18 UTCEG score recompute
  23. 2026-10-09 23:18 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  24. 2026-10-09 20:06 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  25. 2026-10-09 12:16 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  26. 2026-10-08 23:30 UTCEG score recompute
  27. 2026-10-08 23:29 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  28. 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  29. 2026-10-08 12:27 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  30. 2026-10-08 01:21 UTCEG score recompute
  31. 2026-10-08 01:21 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  32. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  33. 2026-10-07 14:19 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  34. 2026-10-07 02:42 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  35. 2026-10-06 15:39 UTCEG score recompute
  36. 2026-10-06 15:39 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  37. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  38. 2026-10-06 04:12 UTCEG score recompute
  39. 2026-10-06 04:12 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  40. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  41. 2026-10-05 17:09 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  42. 2026-10-05 06:08 UTCEG score recompute
  43. 2026-10-05 06:08 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  44. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  45. 2026-10-04 19:06 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  46. 2026-10-04 08:04 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  47. 2026-10-03 21:02 UTCEG score recompute
  48. 2026-10-03 21:02 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  49. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  50. 2026-10-03 10:00 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  51. 2026-10-02 22:58 UTCEG score recompute
  52. 2026-10-02 22:58 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  53. 2026-10-02 11:55 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  54. 2026-10-02 00:49 UTCEG score recompute
  55. 2026-10-02 00:49 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  56. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  57. 2026-10-01 13:43 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  58. 2026-10-01 02:41 UTCEG score recompute
  59. 2026-10-01 02:41 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  60. 2026-09-30 15:39 UTCEG score recompute
  61. 2026-09-30 15:39 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  62. 2026-09-30 15:02 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  63. 2026-09-30 15:02 UTCEG score recompute
  64. 2026-09-30 15:02 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  65. 2026-09-30 11:36 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  66. 2026-09-30 00:34 UTCEG score recompute
  67. 2026-09-30 00:34 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  68. 2026-09-29 15:20 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  69. 2026-09-29 13:31 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  70. 2026-09-29 02:29 UTCEG score recompute
  71. 2026-09-29 02:29 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  72. 2026-09-28 15:27 UTCEG score recompute
  73. 2026-09-28 15:27 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3
  74. 2026-09-28 13:50 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  75. 2026-09-28 04:26 UTCGHSA enrichmentGHSA-jq5g-c66v-g3r2 · GitHub CVSS 7.3

Frequently asked(5)

What is CVE-2026-100666?
CVE-2026-100666 is a high-severity vulnerability; its CVE record was 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 made public?
CVE-2026-100666 was made public on September 10, 2026: that is the date its CVE record's CNA, VulnCheck, gives for when the vulnerability was made public. The CVE record itself was published on September 26, 2026. EchelonGraph's copy of the record carries a last-modified date of September 30, 2026; the record at its source may have been updated since.
Is CVE-2026-100666 actively exploited?
CVE-2026-100666 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (22nd 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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