CVE-2026-56820Public exploitNetwork attack vector

Certificate validation bypass via mismatched OCSP response

Published Jul 21, 2026 · Updated Jul 21, 2026

OCSP validation bypass in Netty 4.1.135.Final and earlier and 4.2.0.Final through 4.2.15.Final allows remote attackers to trust revoked certificates. OcspClient.validateResponse verifies an OCSP response signature but never compares its CertificateID with the certificate named in the request. Exploitation requires control of the OCSP reply path and a valid GOOD response for another certificate from the same CA, causing a revoked certificate to be accepted.

CVSS severity7.4
High
EPSS probability0.22%
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

OCSP validation bypass in Netty 4.1.135.Final and earlier and 4.2.0.Final through 4.2.15.Final allows remote attackers to trust revoked certificates. OcspClient.validateResponse verifies an OCSP response signature but never compares its CertificateID with the certificate named in the request. Exploitation requires control of the OCSP reply path and a valid GOOD response for another certificate from the same CA, causing a revoked certificate to be accepted.

The record

CVE
CVE-2026-56820
Published
Jul 21, 2026
Updated
Jul 21, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 21, 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

9.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
7.4GitHubCVSS: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-295Improper Certificate Validation
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