# CVE-2026-56821: Netty OcspServerCertificateValidator certificate revocation bypass

Source: https://junglewise.ai/threats/cve-2026-56821-netty-ocspservercertificatevalidator-certificate-revocation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-29. Updated: 2026-07-29  
License: CC BY 4.0 with a link back

CVE-2026-56821 · Severity: high · CVSS 7.4 · Published 2026-07-29

Netty is a widely used networking framework for Java applications. A flaw in its certificate validation component allows an attacker to present an expired security status for a certificate that has actually been revoked. This could allow an attacker to impersonate a trusted service or intercept encrypted communications even after their security credentials have been officially cancelled.

Technologies: [io.netty:netty-handler-ssl-ocsp (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-handler-ssl-ocsp), [Netty Project Netty Handler SSL OCSP](https://junglewise.ai/threats/technologies/netty-handler-ssl-ocsp). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty Project](https://junglewise.ai/threats/vendors/netty-project).

## Quick answers

**Is CVE-2026-56821 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56821 being exploited in the wild.

**How severe is CVE-2026-56821?** High severity, with a CVSS score of 7.4, published 29 July 2026.

**Which products and versions are affected?** io.netty:netty-handler-ssl-ocsp (Maven) ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.16.Final.

**Is there a fix for CVE-2026-56821?** Yes. io.netty:netty-handler-ssl-ocsp (Maven): upgrade to 4.2.16.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56821 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-56821?** Check whether you run io.netty:netty-handler-ssl-ocsp (Maven) or Netty Project Netty Handler SSL OCSP at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- io.netty:netty-handler-ssl-ocsp (Maven): upgrade to 4.2.16.Final or later

  ```sh
  # set io.netty:netty-handler-ssl-ocsp to 4.2.16.Final in your pom.xml or build.gradle
  ```


## Technical details

A vulnerability exists in the OcspServerCertificateValidator#userEventTriggered method where a freshness check failure does not trigger a return statement. Consequently, even if an IllegalStateException is fired due to an out-of-date response, the execution falls through and emits a VALID OcspValidationEvent. Because nonce validation is disabled by default, an on-path attacker can replay a stale 'GOOD' OCSP response to make a revoked certificate appear valid. Additionally, the component may throw a NullPointerException if the getNextUpdate() field is null. The issue is resolved in versions 4.1.136.Final and 4.2.16.Final.

## Affected products

- Netty netty-handler-ssl-ocsp < 4.1.136.Final, >= 4.2.0.Final, < 4.2.16.Final

## Identifiers

- CVE-2026-56821
- GHSA-g7hg-vrcf-mvmr

## Timeline

- 2026-07-14: advisory: GitHub advisory published by maintainers
- 2026-07-28: disclosed: NVD publication date

## References

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

## Related threats

- [Netty TOCTOU race condition in OcspServerCertificateValidator](https://junglewise.ai/threats/cve-2026-56822-netty-toctou-race-condition-in-ocspservercertificatevalidator)
- [Netty OcspClient revocation check bypass via improper CertificateID validation](https://junglewise.ai/threats/cve-2026-56820-netty-ocspclient-revocation-check-bypass-via-improper)