PatchSiren cyber security CVE debrief
CVE-2026-56820 netty CVE debrief
CVE-2026-56820 is a high-severity vulnerability in Netty, a network application framework, that allows for replay attacks due to improper OCSP response validation. The issue affects Netty versions 4.2.0.Final through 4.2.15.Final and prior to 4.1.135.Final. The vulnerability is caused by the `OcspClient` not validating that the `CertificateID` in an OCSP response matches the requested `CertificateID`, which can lead to bypass of revocation checks for another certificate.
- Vendor
- netty
- Product
- Unknown
- CVSS
- HIGH 7.4
- CISA KEV
- Not listed in stored evidence
- Original CVE published
- 2026-07-21
- Original CVE updated
- 2026-07-22
- Advisory published
- 2026-07-21
- Advisory updated
- 2026-07-22
Who should care
Users of Netty versions 4.2.0.Final through 4.2.15.Final and prior to 4.1.135.Final should be aware of this vulnerability and take steps to mitigate it. This includes upgrading to a patched version of Netty, specifically 4.1.136.Final or 4.2.16.Final, and performing inventory checks to identify potentially affected systems.
Technical summary
The vulnerability is caused by the `OcspClient` not validating that the `CertificateID` in an OCSP response matches the requested `CertificateID`. This allows for replay attacks, as a legitimately signed `GOOD` status response for an unrelated certificate issued by the same CA can be accepted, bypassing revocation checks for another certificate. The issue is fixed in versions 4.1.136.Final and 4.2.16.Final.
Defensive priority
High
Recommended defensive actions
- Upgrade to a patched version of Netty, specifically 4.1.136.Final or 4.2.16.Final.
- Perform inventory checks to identify potentially affected systems.
- Implement compensating controls, such as monitoring and exception tracking, to detect potential exploitation attempts.
- Verify the validity of OCSP responses to prevent replay attacks.
- Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
- Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
- Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
Evidence notes
The CVE record was published on 2026-07-21T23:17:52.403Z and has been modified since then. The NVD entry is currently awaiting analysis. The vulnerability has a CVSS score of 7.4 and a severity of HIGH.
Official resources
AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-21T23:17:52.403Z and has not been modified since then.