# CVE-2026-59901: Netty Bzip2Decoder infinite loop denial of service

Source: https://junglewise.ai/threats/cve-2026-59901-netty-bzip2decoder-infinite-loop-denial-of-service  
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-2026-59901 · Severity: high · CVSS 4 · Published 2026-07-29

Netty, a widely used framework for building high-performance network applications, contains a flaw in how it handles compressed data. An attacker can send a specially crafted data stream that forces the application into an infinite loop, effectively freezing the service. This results in a denial-of-service, making the application unresponsive to legitimate users and potentially impacting business operations.

Technologies: [io.netty:netty-codec (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec), [io.netty:netty-codec-compression (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-compression). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty](https://junglewise.ai/threats/vendors/netty).

## Quick answers

**Is CVE-2026-59901 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59901 being exploited in the wild.

**How severe is CVE-2026-59901?** High severity, with a CVSS score of 4, published 29 July 2026.

**Which products and versions are affected?** io.netty:netty-codec (Maven) < 4.1.136.Final, ECOSYSTEM:introduced=0,fixed=4.1.136.Final; io.netty:netty-codec-compression (Maven) >= 4.2.0.Final, < 4.2.16.Final, ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.16.Final; Netty-Codec < 4.1.136.Final; Netty-Codec-Compression >= 4.2.0.Final, < 4.2.16.Final.

**Is there a fix for CVE-2026-59901?** Yes. io.netty:netty-codec (Maven): upgrade to 4.1.136.Final or later; io.netty:netty-codec-compression (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-2026-59901 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59901?** Check whether you run io.netty:netty-codec (Maven), io.netty:netty-codec-compression (Maven), Netty-Codec or one of the others listed 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 (Maven): upgrade to 4.1.136.Final or later

  ```sh
  # set io.netty:netty-codec to 4.1.136.Final in your pom.xml or build.gradle
  ```

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

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


## Technical details

A vulnerability exists in the Bzip2Decoder handler within Netty's compression codec pipeline. The flaw is located in the run-length encoding (RLE) state machine within the Bzip2BlockDecompressor.read() method. By providing a malformed bzip2 stream, a remote unauthenticated attacker can trigger an infinite loop (CWE-835) that permanently captures the event-loop thread. Because Netty relies on a non-blocking event-driven model, hanging an event-loop thread can lead to a complete denial of service for all connections handled by that thread. The issue is resolved in versions 4.1.136.Final and 4.2.16.Final.

## Affected products

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

## Identifiers

- CVE-2026-59901
- GHSA-558v-64gr-wgg4

## Timeline

- 2026-07-14: advisory: GitHub Security Advisory published
- 2026-07-29: disclosed: NVD publication date

## References

- [https://github.com/netty/netty/security/advisories/GHSA-558v-64gr-wgg4](https://github.com/netty/netty/security/advisories/GHSA-558v-64gr-wgg4)

## Related threats

- [Netty Lz4FrameDecoder resource exhaustion](https://junglewise.ai/threats/cve-2026-42583-netty-lz4framedecoder-resource-exhaustion)
- [Netty's decoders vulnerable to DoS via zip bomb style attack](https://junglewise.ai/threats/cve-2025-58057-netty-s-decoders-vulnerable-to-dos-via-zip-bomb-style-attack)
- [SnappyFrameDecoder doesn't restrict chunk length any may buffer skippable chunks in an unnecessary way](https://junglewise.ai/threats/cve-2021-37137-snappyframedecoder-doesn-t-restrict-chunk-length-any-may-buffer)
- [Bzip2Decoder doesn't allow setting size restrictions for decompressed data](https://junglewise.ai/threats/cve-2021-37136-bzip2decoder-doesn-t-allow-setting-size-restrictions-for)