CVE-2026-56821

Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator

HIGH

7.4

CVSS Score

Published: July 28, 2026 at 11:07 PM UTC

Updated: August 7, 2026 at 03:05 PM UTC

1 product affected across 1 vendorNetty

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Severity

HIGH7.4

Exploit prediction

EPSS 0.2%

SSVC

PoC

Description

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response to bypass revocation of a since-revoked certificate. Exploitation can lead to certificate revocation bypass via replay of an expired OCSP response. Any application using OcspServerCertificateValidator is affected; a revoked certificate can be accepted. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Netty · Nettymaven

95%

v < 4.1.136v < 4.1.136.Finalv < 4.2.16.Final4.2.0 ≤ v < 4.2.16

Affected range stops below 4.1.136, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.1.136.Final, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.2.16, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.2.16.Final, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr

References (1)

x_refsource_CONFIRMExploitVendor Advisory

Source: cverecord

https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr

SSVC — Action Prioritization

SSVCPoCNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.4HIGHGitHub_M

Attack Vector: NETWORK
Complexity: HIGH
Privileges: NONE
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: HIGH
Integrity: HIGH
Availability: NONE

Vector?

Quick Info

StatusANALYZED

CWE

CWE-299

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