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CVE-2026-56820

Netty vulnerability

7.4 HIGHPublic exploitEPSS 0.31%
  1. Published21 Jul 2026

Description

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 3.1 breakdown

Attack vectorNetwork
Attack complexityHigh
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Netty≥ 4.2.0 < 4.2.16 · < 4.1.136

Remediation

Fixed in
Netty≥ 4.2.16

References

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Frequently asked

Is CVE-2026-56820 being actively exploited?

CVE-2026-56820 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.31%.

How severe is CVE-2026-56820?

CVE-2026-56820 has a CVSS 3.1 base score of 7.4, rated high. EPSS estimates a 0.31% probability of exploitation.

Which products are affected by CVE-2026-56820?

Affected products include Netty.

How do I fix CVE-2026-56820?

Upgrade affected software to a fixed version, for example Netty 4.2.16 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.