What is CVE-2026-59898?

CVE-2026-59898 is a medium-severity security vulnerability in io.netty:netty-codec-http (maven), affecting versions >= 4.2.0.Final, <= 4.2.15.Final. It is fixed in 4.2.16.Final, 4.1.136.Final.

Which versions of io.netty:netty-codec-http are affected by CVE-2026-59898?

io.netty:netty-codec-http (maven) versions >= 4.2.0.Final, <= 4.2.15.Final is affected.

Is there a fix for CVE-2026-59898?

Yes. CVE-2026-59898 is fixed in 4.2.16.Final, 4.1.136.Final. Upgrade to this version or later.

Is CVE-2026-59898 exploitable, and should I be worried?

Whether CVE-2026-59898 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.

What actually determines whether CVE-2026-59898 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.

CVE-2026-59898 in io.netty:netty-codec-http

Q: Which versions of io.netty:netty-codec-http are affected by CVE-2026-59898?

io.netty:netty-codec-http (maven) versions >= 4.2.0.Final, <= 4.2.15.Final is affected.

Q: Is there a fix for CVE-2026-59898?

Yes. CVE-2026-59898 is fixed in 4.2.16.Final, 4.1.136.Final. Upgrade to this version or later.

Q: Is CVE-2026-59898 exploitable, and should I be worried?

Whether CVE-2026-59898 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.

Q: What actually determines whether CVE-2026-59898 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.

Q: How do I fix CVE-2026-59898?

Upgrade: io.netty:netty-codec-http to 4.2.16.Final or later, io.netty:netty-codec-http to 4.1.136.Final or later.

Summary

Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation

An attacker can force WebSocket upgrade via the lax V07 (or V08) handshaker by sending Sec-WebSocket-Version: 7 and omitting Connection: Upgrade / Upgrade: websocket headers, completing a protocol switch that a proxy would not recognize as an Upgrade request and enabling HTTP request smuggling / protocol-confusion attacks.

Impact

Affected versions

io.netty:netty-codec-http (>= 4.2.0.Final, <= 4.2.15.Final) io.netty:netty-codec-http (< 4.1.136.Final)

Security releases

io.netty:netty-codec-http → 4.2.16.Final (maven) io.netty:netty-codec-http → 4.1.136.Final (maven)

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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Remediation advice

Upgrade the following packages to resolve this vulnerability:

io.netty:netty-codec-http to 4.2.16.Final or later; io.netty:netty-codec-http 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-2026-59898? CVE-2026-59898 is a medium-severity security vulnerability in io.netty:netty-codec-http (maven), affecting versions >= 4.2.0.Final, <= 4.2.15.Final. It is fixed in 4.2.16.Final, 4.1.136.Final.
Which versions of io.netty:netty-codec-http are affected by CVE-2026-59898? io.netty:netty-codec-http (maven) versions >= 4.2.0.Final, <= 4.2.15.Final is affected.
Is there a fix for CVE-2026-59898? Yes. CVE-2026-59898 is fixed in 4.2.16.Final, 4.1.136.Final. Upgrade to this version or later.
Is CVE-2026-59898 exploitable, and should I be worried? Whether CVE-2026-59898 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-2026-59898 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-2026-59898?
- Upgrade io.netty:netty-codec-http to 4.2.16.Final or later
- Upgrade io.netty:netty-codec-http to 4.1.136.Final or later

Other vulnerabilities in io.netty:netty-codec-http

CVE-IDSeverityPackage summary

CVE-2026-59921Mediumio.netty:netty-codec-http: Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder CVE-2026-59899Mediumio.netty:netty-codec-http: Netty: [HttpContentEncoder] Unbounded Per-Connection Queue Growth via HTTP/1.1 Pipelining Leads to Denial of Service CVE-2026-56746Mediumio.netty:netty-codec-http: Netty: Security Control Bypass via CORS Short-Circuit Failure CVE-2026-56745Highio.netty:netty-codec-http: Netty: [SpdyHttpDecoder] ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion CVE-2026-55833Highio.netty:netty-codec-http: Netty SPDY zlib header block continues decoded expansion after maxHeaderSize truncation