CVE-2026-56821 — Security Box Score

CVE · referencelatest edition

Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-56821HIGH

Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   H   N   N  U  H  H  N    7.4   .0014    3.6     —

AFFECTED
  Product  Versions           Fixed
  netty    < 4.1.136.Final –  —

TIMELINE
  Jun 23  Reserved by GitHub_M
  Jul 28  Published (CNA: GitHub_M)
  Jul 29  EXPLOIT PUBLISHED — CVE-2026-56821 (netty). Public exploit reference added.
  Aug 7   EXPLOIT PUBLISHED — CVE-2026-56821 (netty). Public exploit reference added.

CWE-299 · CNA: GitHub_M · CVSS v3.1 · 1 reference · NVD status: Analyzed

Description

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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response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.

Lifecycle

Complete event history — 4 events, chronological
Date	Event	Detail
June 23, 2026	Reserved	Reserved by GitHub_M
July 28, 2026	Published	Published (CNA: GitHub_M)
July 29, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-56821 (netty). Public exploit reference added.
August 7, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-56821 (netty). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
netty	netty	—	< 4.1.136.Final	—

Weaknesses

CWE-299

References (1)

https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr [Exploit, Vendor Advisory]

Authoritative record: CVE-2026-56821 at cve.org

Vendors: netty

Weaknesses: CWE-299

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-56821 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.