CVE-2021-37136

Workarounds

No workarounds other than not using the Bzip2Decoder

References

Relevant code areas:

https://github.com/netty/netty/blob/netty-4.1.67.Final/codec/src/main/java/io/netty/handler/codec/compression/Bzip2Decoder.java#L80
https://github.com/netty/netty/blob/netty-4.1.67.Final/codec/src/main/java/io/netty/handler/codec/compression/Bzip2Decoder.java#L294
https://github.com/netty/netty/blob/netty-4.1.67.Final/codec/src/main/java/io/netty/handler/codec/compression/Bzip2Decoder.java#L305

The Bzip2 decompression decoder function doesn't allow setting size restrictions on the decompressed output data (which affects the allocation size used during decompression).

All users of Bzip2Decoder are affected. The malicious input can trigger an OOME and so a DoS attack

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2021-37136 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.1.68.Final); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2021-37136? CVE-2021-37136 is a high-severity uncontrolled resource consumption vulnerability in io.netty:netty-codec (maven), affecting versions < 4.1.68.Final. It is fixed in 4.1.68.Final. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2021-37136? CVE-2021-37136 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2021-37136?
   • io.netty:netty-codec (maven) (versions < 4.1.68.Final)
   • org.jboss.netty:netty (maven) (versions < 4.0.0)
   • io.netty:netty (maven) (versions < 4.0.0)
4. Is there a fix for CVE-2021-37136? Yes. CVE-2021-37136 is fixed in 4.1.68.Final. Upgrade to this version or later.
5. Is CVE-2021-37136 exploitable, and should I be worried? Whether CVE-2021-37136 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
6. What actually determines whether CVE-2021-37136 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.
7. How do I fix CVE-2021-37136? Upgrade io.netty:netty-codec to 4.1.68.Final or later.