CVE-2026-56821
Netty: Out-of-date OCSP Responses Accepted by OcspServerCertificateValidator
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 Prior to versions 4.1.136.Final and 4.2.16.Final, the OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response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.
INFO
Published Date :
July 29, 2026, 12:16 a.m.
Last Modified :
Aug. 7, 2026, 3:05 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Update Netty to version 4.1.136.Final or later.
- Update Netty to version 4.2.16.Final or later.
- Verify OCSP response validation logic.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-56821.
| URL | Resource |
|---|---|
| https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr | Exploit Vendor Advisory |
| https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr | Exploit Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-56821 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-56821
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-56821 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-56821 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Reanalysis by [email protected]
Aug. 07, 2026
Action Type Old Value New Value Changed CPE Configuration OR *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.1.0 up to (excluding) 4.1.136 *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.2.0 up to (excluding) 4.2.16 OR *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions up to (excluding) 4.1.136 *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.2.0 up to (excluding) 4.2.16 -
Initial Analysis by [email protected]
Aug. 06, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.1.0 up to (excluding) 4.1.136 *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.2.0 up to (excluding) 4.2.16 Added Reference Type GitHub, Inc.: https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr Types: Exploit, Vendor Advisory Added Reference Type CISA-ADP: https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr Types: Exploit, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 31, 2026
Action Type Old Value New Value Changed SSVC {'id': 'CVE-2026-56821', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-29T00:00:00+00:00'} {'id': 'CVE-2026-56821', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-30T03:55:19.093244Z'} -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 30, 2026
Action Type Old Value New Value Changed SSVC {'id': 'CVE-2026-56821', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-29T14:13:18.934922Z'} {'id': 'CVE-2026-56821', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-29T00:00:00+00:00'} -
CVE Modified by [email protected]
Jul. 29, 2026
Action Type Old Value New Value Changed Affected [{'vendor': 'netty', 'product': 'netty', 'versions': [{'status': 'affected', 'version': '< 4.1.136.Final'}, {'status': 'affected', 'version': '>=4.2.0.Final, < 4.2.16.Final'}]}] [{'vendor': 'netty', 'product': 'netty', 'versions': [{'status': 'affected', 'version': '< 4.1.136.Final'}, {'status': 'affected', 'version': '>= 4.2.0.Final, < 4.2.16.Final'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 29, 2026
Action Type Old Value New Value Added Reference https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr Added SSVC {'id': 'CVE-2026-56821', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-29T14:13:18.934922Z'} -
New CVE Received by [email protected]
Jul. 29, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'netty', 'product': 'netty', 'versions': [{'status': 'affected', 'version': '< 4.1.136.Final'}, {'status': 'affected', 'version': '>=4.2.0.Final, < 4.2.16.Final'}]}] Added 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N Added CWE CWE-299 Added Reference https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr