Vulnerability in Netty
CVE-2026-56821
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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response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.
EPSS: 0.002 (5.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N.
Affected products
- Netty — versions >= 4.2.0.Final, < 4.2.16.Final, >=4.2.0.Final, < 4.2.16.Final, < 4.1.136.Final
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-56821?
- CVE-2026-56821 is a high-severity vulnerability in Netty, classified under Improper Check for Certificate Revocation. CVSS score: 7.4/10. Published 2026-07-29.
- How severe is CVE-2026-56821?
- High severity. CVSS v3 base score is 7.4 out of 10.