Review reviewCritical

CVE-2026-56820

netty

Netty is a network application framework for development of protocol servers and clients. In versions 4.2.0.Final through 4.2.15.Final and prior to 4.1.135.Final, `OcspClient` does not validate that the `CertificateID` in an OCSP response matches the requested `CertificateID`, which can lead to replay attack. `OcspClient.validateResponse` accepts a legitimately signed `GOOD` status response for an unrelated certificate issued by the same CA, allowing bypass of revocation checks for another certificate. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

CVSS: 9.1
EPSS: -
CISA KEV: Not listed
Published: 2026.07.22

PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability-

Technical severityCVSS 9.1

Vulnerability overview

Affected product and versions

Product: netty
Affected versions: >= >= 4.2.0.Final, < 4.2.16.Final, >= < 4.1.136.Final, < 4.1.136, >= 4.2.0 < 4.2.16
Fixed versions: 4.1.136, 4.2.16

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that netty and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CWE: CWE-295