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CVE-2026-56821— Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator

Quick assessment

Affected
netty netty
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Netty是Netty团队开源的一款非阻塞I/O客户端-服务器框架,它主要用于开发Java网络应用程序,如协议服务器和客户端等。 Netty 4.1.136.Final之前版本和4.2.0.Final至4.2.16.Final之前版本存在加密问题漏洞，该漏洞源于OcspServerCertificateValidator对过期的OCSP响应处理不当，导致攻击者可通过重放过期的OCSP响应绕过证书撤销，使得已吊销的证书仍可被接受。

CVSS 7.4 · High EPSS 0.22% · P11

Possible ATT&CK Techniques 1 AI

T1557.002 · ARP Cache Poisoning

Affected Version Matrix 2

VendorProduct Version RangeStatus
netty netty < 4.1.136.Final affected
>= 4.2.0.Final, < 4.2.16.Final affected
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I. Basic Information for CVE-2026-56821

Vulnerability Information
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Vulnerability Title
Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator
Source: CVE Program / CVE List V5
Vulnerability 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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
证书撤销验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Netty 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Netty是Netty团队开源的一款非阻塞I/O客户端-服务器框架,它主要用于开发Java网络应用程序,如协议服务器和客户端等。 Netty 4.1.136.Final之前版本和4.2.0.Final至4.2.16.Final之前版本存在加密问题漏洞，该漏洞源于OcspServerCertificateValidator对过期的OCSP响应处理不当，导致攻击者可通过重放过期的OCSP响应绕过证书撤销，使得已吊销的证书仍可被接受。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
netty netty < 4.1.136.Final -

II. Public POCs for CVE-2026-56821

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 12257 chars
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In-depth vulnerability mechanism
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III. Intelligence Information for CVE-2026-56821

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Vendor Advisories for CVE-2026-56821 (1)

Same Patch Batch · netty · 2026-07-28 · 3 CVEs total

CVE-2026-56822 7.4 HIGH Netty: TOCTOU in OcspServerCertificateValidator
CVE-2026-59921 5.7 MEDIUM Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder

IV. Related Vulnerabilities

Same product: netty
Same vendor: netty
Same weakness: CWE-299

V. Comments for CVE-2026-56821

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