# CVE-2026-93558: Netty WebSocketServerExtensionHandler denial of service

Source: https://junglewise.ai/threats/cve-2026-93558-netty-websocketserverextensionhandler-denial-of-service  
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-2026-93558 · Severity: high · CVSS 7.5 · Published 2026-09-18

Netty is an open-source Java networking library used by many applications to handle high-performance network communication. A vulnerability in its WebSocket handler allows an unauthenticated attacker to send specially crafted HTTP requests that accumulate in a queue faster than the server can process them, eventually exhausting the server's memory and causing it to crash, resulting in service downtime.

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

## Quick answers

**Is CVE-2026-93558 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93558 being exploited in the wild.

**How severe is CVE-2026-93558?** High severity, with a CVSS score of 7.5, published 18 September 2026.

**Which products and versions are affected?** Netty <UNKNOWN>.

**Is there a fix for CVE-2026-93558?** 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-2026-93558 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-93558?** Check whether you run Netty 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.

## Technical details

The vulnerability exists in Netty's WebSocketServerExtensionHandler component and involves improper handling of HTTP/1.1 pipelined requests. An attacker can exploit this by sending multiple HTTP requests in rapid succession over a single connection, causing them to queue unbounded in memory. The handler fails to properly limit queue growth, leading to heap exhaustion in the Java Virtual Machine and a denial-of-service condition. No authentication is required; the attack is triggered via network-accessible HTTP requests. A patch addressing queue management should be available from the Netty project.

## Affected products

- Netty Netty <UNKNOWN>

## 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 HTTP request smuggling via control characters in chunk size](https://junglewise.ai/threats/cve-2026-93566-netty-http-request-smuggling-via-control-characters-in-chunk-size)
- [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)