CVE-2026-56821

HIGHPre-NVD 7.47.4—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.4 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 94% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Elevated
7.4EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.4Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response to bypass revocation of a since-revoked certificate. Exploitation can lead to certificate revocation bypass via replay of an expired OCSP response. Any application using OcspServerCertificateValidator is affected; a revoked certificate can be accepted. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

CVSS v3
7.4
EG Score
7.4(medium)
EG Risk
49(Track*)
EG Risk 49/100SSVC: Track*

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
Severity74% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
0%
EPSS %ILE
6%
KEV
Not listed

Published

July 22, 2026

Last Modified

August 7, 2026

Advisory Details (1)

Auto-updated Jul 28, 2026
🔬 Proof of concept available. Patch available. Sources: github.
github Patch Available🟡 PoC Available

Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator · Advisory · netty/netty · GitHub

https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr

Vendor Advisories for CVE-2026-56821(1)

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

Affected Packages

(5 across 5 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
netty1:4.1.48-10 ... 1:4.1.48-9 (16 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
netty1:4.1.48-10 ... 1:4.1.48-9 (12 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
netty1:4.1.48-10 ... 1:4.1.48-16 (8 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
netty1:4.1.48-10 ... 1:4.1.48-16 (7 versions)——
Maven(1)
PackageVulnerable rangeFixed inDependents
io.netty:netty-handler-ssl-ocsp4.1.100.Final ... 4.1.99.Final (50 versions)4.1.136.Final—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 9× in last 7d / 47× 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. 2026-09-15 03:11 UTCEPSS rescore
  2. 2026-09-13 16:51 UTCEG score recompute
  3. 2026-09-13 16:47 UTCEPSS rescore
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  1. 2026-08-30 00:50 UTCEG score recompute
  2. 2026-08-28 21:42 UTCEPSS rescore
  3. 2026-08-27 21:28 UTCEG score recompute
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  20. 2026-08-18 13:48 UTCEPSS rescore
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  26. 2026-08-16 02:14 UTCEPSS rescore
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  30. 2026-08-13 22:00 UTCEPSS rescore
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  35. 2026-08-11 00:00 UTCEPSS rescore
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  37. 2026-08-08 16:37 UTCEPSS rescore
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  39. 2026-08-06 18:16 UTCEG score recompute
  40. 2026-08-06 13:47 UTCEPSS rescore
  41. 2026-08-05 19:53 UTCEG score recompute
  42. 2026-08-05 19:17 UTCEPSS rescore
  43. 2026-08-04 21:27 UTCEG score recompute
  44. 2026-08-04 15:10 UTCEPSS rescore
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  50. 2026-08-01 14:53 UTCEG score recompute
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  53. 2026-07-31 16:26 UTCEG score recompute
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  55. 2026-07-30 16:28 UTCEPSS rescore
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  58. 2026-07-30 01:30 UTCEPSS rescore
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  60. 2026-07-29 18:31 UTCEG score recompute
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  63. 2026-07-29 14:49 UTCEG score recompute
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  65. 2026-07-26 21:00 UTCEG score recompute
  66. 2026-07-23 03:20 UTCEG score recompute
  67. 2026-07-22 22:27 UTCEG score recompute

Frequently asked(5)

What is CVE-2026-56821?
CVE-2026-56821 is a high vulnerability published on July 22, 2026. Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path…
When was CVE-2026-56821 disclosed?
CVE-2026-56821 was first published in the National Vulnerability Database on July 22, 2026, with the most recent update on August 7, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-56821 actively exploited?
CVE-2026-56821 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 94.1% of all scored CVEs.
What is the CVSS score of CVE-2026-56821?
CVE-2026-56821 has a CVSS v3 base score of 7.4 (NVD).
How do I remediate CVE-2026-56821?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-56821, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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