# CVE-2026-59899: Netty resource exhaustion in HttpContentEncoder via HTTP pipelining

Source: https://junglewise.ai/threats/cve-2026-59899-netty-resource-exhaustion-in-httpcontentencoder-via-http  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-29. Updated: 2026-07-29  
License: CC BY 4.0 with a link back

CVE-2026-59899 · Severity: medium · CVSS 4 · Published 2026-07-29

Netty, a popular framework for building network applications, contains a flaw in how it handles certain web requests. An attacker can send a flood of specially crafted messages that cause the application to consume excessive memory, potentially leading to a system crash or service outage. This impacts the availability of any service built using the affected versions of the Netty library.

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-2026-59899 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59899 being exploited in the wild.

**How severe is CVE-2026-59899?** Medium severity, with a CVSS score of 4, published 29 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.

**Is there a fix for CVE-2026-59899?** 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-2026-59899 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59899?** 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 resource exhaustion vulnerability exists in Netty's HttpContentEncoder (and its subclass HttpContentCompressor). The component maintains a per-channel ArrayDeque called 'acceptEncodingQueue' that stores attacker-controlled CharSequence data without a size limit. By utilizing HTTP/1.1 pipelining, a remote unauthenticated attacker can flood a connection with requests faster than the application can generate non-1xx responses, causing the queue to grow indefinitely and exhaust heap memory. This issue is resolved in versions 4.1.136.Final and 4.2.16.Final.

## Affected products

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

## Identifiers

- CVE-2026-59899
- GHSA-q4f6-jm68-57ww

## Timeline

- 2026-07-07: patched: Version 4.2.16.Final released
- 2026-07-08: patched: Version 4.1.136.Final released
- 2026-07-14: advisory: GitHub Security Advisory GHSA-q4f6-jm68-57ww published
- 2026-07-29: disclosed: NVD publication date

## References

- [https://github.com/netty/netty/releases/tag/netty-4.1.136.Final](https://github.com/netty/netty/releases/tag/netty-4.1.136.Final)
- [https://github.com/netty/netty/releases/tag/netty-4.2.16.Final](https://github.com/netty/netty/releases/tag/netty-4.2.16.Final)
- [https://github.com/netty/netty/security/advisories/GHSA-q4f6-jm68-57ww](https://github.com/netty/netty/security/advisories/GHSA-q4f6-jm68-57ww)

## 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 CRLF injection in HttpPostRequestEncoder multipart filenames](https://junglewise.ai/threats/cve-2026-59921-netty-crlf-injection-in-httppostrequestencoder-multipart)
- [Netty security bypass in CorsHandler origin evaluation](https://junglewise.ai/threats/cve-2026-56746-netty-security-bypass-in-corshandler-origin-evaluation)