CVE-2026-56821Public exploitNetwork attack vector

Certificate revocation bypass via stale OCSP replay

Published Jul 28, 2026 · Updated Jul 28, 2026

Revocation bypass in Netty before 4.1.136.Final or 4.2.0.Final through 4.2.15.Final allows attackers to accept revoked certificates. OcspServerCertificateValidator.userEventTriggered reports an out-of-date response but, lacking a return after the freshness check, falls through and fires a VALID OcspValidationEvent. Man-in-the-middle attackers can replay a stale GOOD response when an application uses this validator; nonce validation is optional and disabled by default.

CVSS severity7.4
High
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Revocation bypass in Netty before 4.1.136.Final or 4.2.0.Final through 4.2.15.Final allows attackers to accept revoked certificates. OcspServerCertificateValidator.userEventTriggered reports an out-of-date response but, lacking a return after the freshness check, falls through and fires a VALID OcspValidationEvent. Man-in-the-middle attackers can replay a stale GOOD response when an application uses this validator; nonce validation is optional and disabled by default.

The record

CVE
CVE-2026-56821
Published
Jul 28, 2026
Updated
Jul 28, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-299, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.1.136.Final
  2. Affected versionversion=>=4.2.0.Final, < 4.2.16.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Netty Project · Nettyversion=< 4.1.136.Final; version=>=4.2.0.Final, < 4.2.16.Final

Published CVSS scores

7.4GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-299Improper Check for Certificate Revocation
T1557Adversary-in-the-Middle

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo