# CVE-2026-93566: Netty HTTP request smuggling via control characters in chunk size

Source: https://junglewise.ai/threats/cve-2026-93566-netty-http-request-smuggling-via-control-characters-in-chunk-size  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-18. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-93566 · Severity: medium · CVSS 6.5 · Published 2026-09-18

Netty is a popular networking library used in many Java applications to handle HTTP requests. An attacker can send a specially crafted HTTP request containing control characters in the chunk-size field to bypass validation checks, leading to HTTP request smuggling attacks. This could allow an attacker to inject unauthorized requests, potentially exposing sensitive data or bypassing security controls.

Technologies: [Netty](https://junglewise.ai/threats/technologies/netty). Vendors: [Netty](https://junglewise.ai/threats/vendors/netty).

## Quick answers

**Is CVE-2026-93566 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93566 being exploited in the wild.

**How severe is CVE-2026-93566?** Medium severity, with a CVSS score of 6.5, published 18 September 2026.

**Which products and versions are affected?** Netty Netty.

**Is there a fix for CVE-2026-93566?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-93566 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-93566?** Check whether you run Netty. 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.

## Technical details

The vulnerability is an HTTP request smuggling flaw (CWE-444) in Netty's HTTP chunk decoding logic. The root cause is insufficient validation of control characters within the chunk-size line of chunked transfer encoding. A remote, unauthenticated attacker can send a crafted HTTP request that exploits this validation bypass to inject arbitrary HTTP requests. The attack vector is network-based and requires no authentication or special preconditions. Successful exploitation can lead to request smuggling, information disclosure, and unauthorized actions. Patches are expected from the Netty project.

## Affected products

- Netty Netty

## Timeline

- 2026-09-18: disclosed

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/jbossnetwork/restricted/listSoftware.html](https://access.redhat.com/jbossnetwork/restricted/listSoftware.html)

## Related threats

- [Netty HTTP/1 decoder request smuggling](https://junglewise.ai/threats/cve-2026-93562-a-flaw-was-found-in-netty-s-http-1-decoder-incomplete-validation)
- [Netty HTTP/1 to HTTP/2 conversion authority mismatch](https://junglewise.ai/threats/cve-2026-93569-netty-http-1-to-http-2-conversion-authority-mismatch)
- [Netty RtspDecoder method-token smuggling in RTSP parsing](https://junglewise.ai/threats/cve-2026-93565-netty-rtspdecoder-method-token-smuggling-in-rtsp-parsing)
- [Netty reference-count leak in HAProxy PROXY-v2 decoder](https://junglewise.ai/threats/cve-2026-93564-netty-reference-count-leak-in-haproxy-proxy-v2-decoder)
- [Netty WebSocketServerExtensionHandler denial of service](https://junglewise.ai/threats/cve-2026-93558-netty-websocketserverextensionhandler-denial-of-service)