CVE-2026-56821

Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator

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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD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

netty

CVSS v3.1 GITHUB

7.4 HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

0.22% chance of exploitation in the next 30 days, 12th percentile

Published

2026-07-28

Updated

2026-07-31

Proof-of-concept exploits (1)

• advisories/GHSA-g7hg-vrcf-mvmr

Security advisories

• netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr

References

• CVE Record
• NVD entry