CVE-2026-75596

HIGHNVD 7.57.5
EchelonGraph scoreMEDIUM confidence

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

This high-severity CVE scores 7.5 under NVD CVSS v3. EPSS exploit probability: 0.4% (31st percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
Trending — 3 sources updated this week

Also known asEUVD-2026-63092 (ENISA EUVD) · GHSA-fccg-mwvh-qqg4 (GitHub Security Advisories)Source: ENISA EUVD

7.5EG
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).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 7.5Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at io.netty.handler.ssl.SslClientHelloHandler#decode, where handshakeBuffer.clear() and writeBytes() recopy all previously received body bytes for every additional TLS record. An unauthenticated remote peer can advertise a large ClientHello and deliver its body in thousands of tiny records, causing quadratic CPU work on the event loop before the TLS handshake completes and degrading TLS handling for other clients. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

CVSS v3
7.5
EG Score
7.5HIGHmedium confidence
EG Risk
49
EG Risk 49/100

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)
Severity75% × 45%
Impact severity (EG Severity): CVSS 7.5 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.4% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
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 none (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
0.4%
EPSS %ILE
31st
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 (7.5): severity, escalated by confirmed exploitation. This CVE's 7.5 is its impact severity (EG Severity), not escalated.

EG Severity
7.5 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-31). 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 none (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

August 19, 2026

Last Modified

October 26, 2026

Advisory Details (7)

Auto-updated Aug 19, 2026
Patch available. Sources: github, github_pr, github_commit, github_release.
GitHub release Patch Available

netty-4.2.17.Final

Patch available: netty/netty netty-4.2.17.Final

https://github.com/netty/netty/releases/tag/netty-4.2.17.Final
GitHub release Patch Available

netty-4.1.137.Final

Patch available: netty/netty netty-4.1.137.Final

https://github.com/netty/netty/releases/tag/netty-4.1.137.Final
GitHub commit Patch Available

commit 9e0519239108 (netty/netty)

Patch available: netty/netty netty-4.1.137.Final (contains commit 9e0519239108)

https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961
GitHub commit Patch Available

commit 1b5abc6443b6 (netty/netty)

Patch available: netty/netty netty-4.2.17.Final (contains commit 1b5abc6443b6)

https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7
GitHub pull request Patch Available

Merge changes from forks (#17213)

Patch available: netty/netty netty-4.1.137.Final (PR #17217 merged 2026-08-06)

https://github.com/netty/netty/pull/17217
GitHub pull request Patch Available

Merge changes from forks

Patch available: netty/netty netty-4.2.17.Final (PR #17213 merged 2026-08-04)

https://github.com/netty/netty/pull/17213
GitHub advisoryMentions a patch (unverified)

Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing · Advisory · netty/netty · GitHub

https://github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4

Vendor Advisories for CVE-2026-75596(1)

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

Patch Availability(2)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
mavenio.netty:netty-handler @ 4.2.17.Final (fixes >= 4.2.0.Final, <= 4.2.16.Final)—ghsa
mavenio.netty:netty-handler @ 4.1.137.Final (fixes <= 4.1.136.Final)—ghsa

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

(4 across 4 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
—
Maven(1)
PackageVulnerable rangeFix by version rangeDependents
io.netty:netty-handler4.0.0.Alpha1 ... 4.1.99.Final (230 versions)
  • 4.2.0.Final up to 4.2.17.Final: fixed in 4.2.17.Final
  • every version up to 4.1.137.Final: fixed in 4.1.137.Final
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 11× in last 7d / 47× 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 130 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 30 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  2. 2026-11-01 07:39 UTCGHSA enrichmentGHSA-fccg-mwvh-qqg4 · GitHub severity MODERATE
  3. 2026-11-01 07:39 UTCEG score recompute
  4. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  5. 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  6. 2026-10-29 16:34 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  7. 2026-10-28 16:33 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  8. 2026-10-27 21:09 UTCEG score recompute
  9. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  10. 2026-10-26 16:32 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  11. 2026-10-26 10:26 UTCEG score recompute
  12. 2026-10-25 16:34 UTCEPSS rescoreEPSS 0.4% · 31st percentile
  13. 2026-10-25 14:02 UTCEG score recompute
  14. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  15. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  16. 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  17. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  18. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  19. 2026-10-20 11:00 UTCEG score recompute
  20. 2026-10-19 16:33 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  21. 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  22. 2026-10-18 03:13 UTCEG score recompute
  23. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  24. 2026-10-16 16:44 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  25. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
Show 75 more
  1. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  2. 2026-10-13 16:35 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  3. 2026-10-13 07:20 UTCEG score recompute
  4. 2026-10-12 16:35 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  5. 2026-10-12 15:39 UTCEG score recompute
  6. 2026-10-11 19:24 UTCEG score recompute
  7. 2026-10-11 16:40 UTCEG score recompute
  8. 2026-10-11 13:59 UTCEG score recompute
  9. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  10. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  11. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  12. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  13. 2026-10-08 06:16 UTCEG score recompute
  14. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  15. 2026-10-06 19:31 UTCEG score recompute
  16. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  17. 2026-10-06 07:54 UTCEG score recompute
  18. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  19. 2026-10-05 05:07 UTCEG score recompute
  20. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  21. 2026-10-03 16:53 UTCEG score recompute
  22. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  23. 2026-10-02 22:00 UTCEG score recompute
  24. 2026-10-01 22:45 UTCEG score recompute
  25. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  26. 2026-09-30 20:33 UTCEG score recompute
  27. 2026-09-30 08:35 UTCEG score recompute
  28. 2026-09-29 15:24 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  29. 2026-09-28 21:41 UTCEG score recompute
  30. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  31. 2026-09-27 16:08 UTCEG score recompute
  32. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  33. 2026-09-27 04:22 UTCEG score recompute
  34. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  35. 2026-09-26 00:28 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  36. 2026-09-24 19:31 UTCEG score recompute
  37. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  38. 2026-09-23 20:07 UTCEG score recompute
  39. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  40. 2026-09-22 19:33 UTCEG score recompute▼ 1.20
  41. 2026-09-22 19:32 UTCNVD updateCVSS v3 → 7.5
  42. 2026-09-22 16:01 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  43. 2026-09-22 08:13 UTCEG score recompute
  44. 2026-09-21 21:09 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  45. 2026-09-20 21:10 UTCEG score recompute
  46. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  47. 2026-09-19 21:52 UTCEG score recompute
  48. 2026-09-18 21:41 UTCEG score recompute
  49. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  50. 2026-09-17 21:28 UTCEG score recompute
  51. 2026-09-16 20:05 UTCEG score recompute
  52. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  53. 2026-09-16 06:28 UTCEG score recompute
  54. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  55. 2026-09-15 06:50 UTCEG score recompute
  56. 2026-09-15 03:12 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  57. 2026-09-13 19:31 UTCEG score recompute
  58. 2026-09-12 20:17 UTCEG score recompute
  59. 2026-09-12 15:02 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  60. 2026-09-11 21:03 UTCEG score recompute
  61. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  62. 2026-09-10 10:11 UTCEG score recompute
  63. 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  64. 2026-09-09 02:14 UTCEG score recompute
  65. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  66. 2026-09-07 21:44 UTCEG score recompute
  67. 2026-09-06 22:24 UTCEG score recompute
  68. 2026-09-06 13:48 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  69. 2026-09-05 23:09 UTCEG score recompute
  70. 2026-09-04 23:54 UTCEG score recompute
  71. 2026-09-04 11:44 UTCEG score recompute
  72. 2026-09-04 05:07 UTCEPSS rescoreEPSS 0.4% · 27th percentile
  73. 2026-09-03 00:29 UTCEG score recompute
  74. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.4% · 27th percentile
  75. 2026-09-02 01:06 UTCEG score recompute

Frequently asked(5)

What is CVE-2026-75596?
CVE-2026-75596 is a high-severity vulnerability; its CVE record was published on August 19, 2026. Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at…
When was the CVE record for CVE-2026-75596 published?
The CVE record for CVE-2026-75596 was published on August 19, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of October 26, 2026; the record at its source may have been updated since.
Is CVE-2026-75596 actively exploited?
CVE-2026-75596 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (31st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-75596?
CVE-2026-75596 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-75596?
A fix for CVE-2026-75596 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-75596 are linked in the Vendor Advisories panel on this page.

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