Vulnerability · Published Jul 28, 2026 · Assigned by GitHub_M
CVE-2026-56821Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator
High 7.4
In plain English
A high-severity security flaw in netty from netty. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 12% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | netty | no fix listed | DEBIAN-CVE-2026-56821 |
| Debian:13 | netty | no fix listed | DEBIAN-CVE-2026-56821 |
| Debian:14 | netty | no fix listed | DEBIAN-CVE-2026-56821 |
| Maven | io.netty:netty-handler-ssl-ocsp | 4.2.16.Final | GHSA-g7hg-vrcf-mvmr |
| Maven | io.netty:netty-handler-ssl-ocsp | 4.1.136.Final | GHSA-g7hg-vrcf-mvmr |
| Ubuntu:26.10 | netty | no fix listed | UBUNTU-CVE-2026-56821 |
Affected products (as reported)
Weakness: CWE-299 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
References
- https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr x_refsource_CONFIRM