Summary
Netty: [Bzip2Decoder] Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang
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()]
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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io.netty:netty-codec-compression to 4.2.16.Final or later; io.netty:netty-codec to 4.1.136.Final or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-59901? CVE-2026-59901 is a high-severity security vulnerability in io.netty:netty-codec-compression (maven), affecting versions >= 4.2.0.Final, < 4.2.16.Final. It is fixed in 4.2.16.Final, 4.1.136.Final.
- Which packages are affected by CVE-2026-59901?
io.netty:netty-codec-compression(maven) (versions >= 4.2.0.Final, < 4.2.16.Final)io.netty:netty-codec(maven) (versions < 4.1.136.Final)
- Is there a fix for CVE-2026-59901? Yes. CVE-2026-59901 is fixed in 4.2.16.Final, 4.1.136.Final. Upgrade to this version or later.
- Is CVE-2026-59901 exploitable, and should I be worried? Whether CVE-2026-59901 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59901 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59901?
- Upgrade
io.netty:netty-codec-compressionto 4.2.16.Final or later - Upgrade
io.netty:netty-codecto 4.1.136.Final or later
- Upgrade