CVE-2026-56820: 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

highCVSS 7.4CVE-2026-56820

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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: high — CVSS 7.4
Published: 2026-07-21
Last updated: 2026-07-24
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-56820

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-568200.18% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 8% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-56820	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for Netty is a

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highGHSA-93wv-jw9v-4972: Netty: HTTP/2 decompression leaks ByteBuf reference count when the decompressor channel i…ghsa · 2026-07-31
medium[NEW] [medium] Netty: Multiple vulnerabilitiescert-bund · 2026-07-30
high[NEW] [high] Netty: Multiple vulnerabilitiescert-bund · 2026-07-30
high[UPDATE] [high] Netty: Multiple vulnerabilitiescert-bund · 2026-07-30
unknownCVE-2026-59898: Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.13…nvd · 2026-07-29
mediumCVE-2026-59920: Netty is an asynchronous, event-driven network application framework. In versions prior to 4.1…nvd · 2026-07-29