# CVE-2026-56821

## Summary

- **CVE ID:** CVE-2026-56821
- **Severity:** HIGH
- **CVSS Score:** 7.4 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N)
- **CWE:** CWE-299
- **Published:** Jul 28, 2026
- **Last Modified:** Jul 31, 2026

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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD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

- netty — netty (< 4.1.136.Final)
- netty — netty (>=4.2.0.Final, < 4.2.16.Final)
- netty — netty (>= 4.2.0.Final, < 4.2.16.Final)

## References

- [CNA](https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.16%
- **EPSS Percentile:** 5.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._