# CVE-2026-56746: Netty security bypass in CorsHandler origin evaluation

Source: https://junglewise.ai/threats/cve-2026-56746-netty-security-bypass-in-corshandler-origin-evaluation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-21. Updated: 2026-07-22  
License: CC BY 4.0 with a link back

CVE-2026-56746 · Severity: medium · CVSS 6.5 · Published 2026-07-21

Netty, a widely used networking framework for Java applications, contains a flaw in its Cross-Origin Resource Sharing (CORS) protection mechanism. This security feature is intended to block unauthorized web requests from reaching a backend application. An attacker can bypass these restrictions, potentially allowing unauthorized web-based interactions with the application that should have been blocked.

Technologies: [io.netty:netty-codec-http (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http), [Netty Project Codec HTTP](https://junglewise.ai/threats/technologies/codec-http). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty Project](https://junglewise.ai/threats/vendors/netty-project).

## Quick answers

**Is CVE-2026-56746 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56746 being exploited in the wild.

**How severe is CVE-2026-56746?** Medium severity, with a CVSS score of 6.5, published 21 July 2026.

**Which products and versions are affected?** io.netty:netty-codec-http (Maven) ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.16.Final; Netty Project Codec HTTP 4.1.0.Final to 4.1.135.Final, 4.2.0.Final to 4.2.15.Final.

**Is there a fix for CVE-2026-56746?** Yes. io.netty:netty-codec-http (Maven): upgrade to 4.2.16.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56746 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-56746?** Check whether you run io.netty:netty-codec-http (Maven), Netty Project Codec HTTP or Netty Project Netty codec-http at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- io.netty:netty-codec-http (Maven): upgrade to 4.2.16.Final or later

  ```sh
  # set io.netty:netty-codec-http to 4.2.16.Final in your pom.xml or build.gradle
  ```


## Technical details

A logic error exists in io.netty.handler.codec.http.cors.CorsHandler where the short-circuit mechanism, intended to reject unauthorized origins before they reach the backend, can be bypassed. The getForOrigin method incorrectly returns a configuration object when an 'Origin: null' header is received, regardless of whether the developer has explicitly allowed null origins via isNullOriginAllowed(). This causes the short-circuit check to evaluate as false, forwarding the unauthorized request to the backend application. The vulnerability is tracked as CVE-2026-56746 and is resolved in versions 4.1.136.Final and 4.2.16.Final.

## Affected products

- Netty netty-codec-http >= 4.2.0.Final, < 4.2.16.Final; < 4.1.136.Final

## Identifiers

- CVE-2026-56746
- GHSA-6cqp-g7gg-8hr5

## Timeline

- 2026-07-20: disclosed
- 2026-07-21: advisory: NVD publication date
- 2026-07-22: patched: GitHub Advisory published/reviewed

## References

- [https://api.github.com/users/violetagg](https://api.github.com/users/violetagg)
- [https://github.com/violetagg](https://github.com/violetagg)
- [https://api.github.com/users/violetagg/gists%7B/gist_id%7D](https://api.github.com/users/violetagg/gists%7B/gist_id%7D)
- [https://api.github.com/users/violetagg/repos](https://api.github.com/users/violetagg/repos)
- [https://avatars.githubusercontent.com/u/696661?v=4](https://avatars.githubusercontent.com/u/696661?v=4)
- [https://api.github.com/users/violetagg/events%7B/privacy%7D](https://api.github.com/users/violetagg/events%7B/privacy%7D)

## Related threats

- [Netty HttpServerCodec response desynchronization](https://junglewise.ai/threats/cve-2026-100666-netty-s-httpservercodec-io-netty-netty-codec-http-in-versions-4)
- [Netty CorsHandler cache poisoning via Vary header overwrite](https://junglewise.ai/threats/cve-2026-59903-netty-corshandler-cache-poisoning-via-vary-header-overwrite)
- [Netty HTTP request smuggling via lax WebSocket handshake validation](https://junglewise.ai/threats/cve-2026-59898-netty-http-request-smuggling-via-lax-websocket-handshake)
- [Netty resource exhaustion in HttpContentEncoder via HTTP pipelining](https://junglewise.ai/threats/cve-2026-59899-netty-resource-exhaustion-in-httpcontentencoder-via-http)
- [Netty CRLF injection in HttpPostRequestEncoder multipart filenames](https://junglewise.ai/threats/cve-2026-59921-netty-crlf-injection-in-httppostrequestencoder-multipart)