CVE-2026-56821: Netty

High severity, CVSS 7.4. EPSS: 0.2% chance of exploitation in the next 30 days.

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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD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

Affected products

• Netty Netty: before 4.1.136 (fixed in 4.1.136); from 4.2.0, before 4.2.16 (fixed in 4.2.16)

Published 2026-07-29. Last modified 2026-08-07.