Vulnerability record · CVE-2026-56820 · published 21 July 2026

CVE-2026-56820: Netty improper certificate validation vulnerability

Netty · 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.

9.1 CVSS 3.1 Critical EPSS 0.31% · top 78.3% CWE-295 · Improper certificate validation

9.1CVSS 3.1 base score

0.31%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

5References, 1 tagged exploit

30 Jul 2026Last modified by NVD

Description

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

Netty Netty

References

Link	Tags
https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b	Patch
https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6	Patch
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final	Release Notes
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final	Release Notes
https://github.com/netty/netty/security/advisories/GHSA-272m-gcwp-mpwg	ExploitVendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-56820), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.