CVE-2026-42585 is a medium-severity security vulnerability in io.netty:netty-codec-http (maven), affecting versions >= 4.2.0.Alpha1, <= 4.2.12.Final. It is fixed in 4.2.13.Final, 4.1.133.Final.
Summary Netty incorrectly parses malformed Transfer-Encoding, enabling request smuggling attacks. Details Netty incorrectly marks a request as chunked when malformed "Transfer-Encoding: chunked, identity" is present. According to RFC https://datatracker.ietf.org/doc/html/rfc9112#name-message-body-length " If a Transfer-Encoding header field is present in a request and the chunked transfer coding is not the final encoding, the message body length cannot be determined reliably; the server MUST respond with the 400 (Bad Request) status code and then close the connection. " A possible scenario is when Netty is behind a proxy that doesn't reject requests with "Transfer-Encoding: chunked, identity", but prefers "Content-Length" and forwards the content to Netty. PoC The test below shows Netty successfully parsing the second request, demonstrating how an attacker can smuggle a second request inside a request body. Impact HTTP Request Smuggling: Attacker injects arbitrary HTTP requests
CVE-2026-42585 has a CVSS score of 6.5 (Medium). 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 (4.2.13.Final, 4.1.133.Final). Upgrading removes the vulnerable code path.
maven
io.netty:netty-codec-http (>= 4.2.0.Alpha1, <= 4.2.12.Final)io.netty:netty-codec-http (<= 4.1.132.Final)io.netty:netty-codec-http → 4.2.13.Final (maven)io.netty:netty-codec-http → 4.1.133.Final (maven)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 instead of chasing every advisory.
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Upgrade the following packages to resolve this vulnerability:
io.netty:netty-codec-http to 4.2.13.Final or laterio.netty:netty-codec-http to 4.1.133.Final or laterKodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-42585 is a medium-severity security vulnerability in io.netty:netty-codec-http (maven), affecting versions >= 4.2.0.Alpha1, <= 4.2.12.Final. It is fixed in 4.2.13.Final, 4.1.133.Final.
CVE-2026-42585 has a CVSS score of 6.5 (Medium). 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.
io.netty:netty-codec-http (maven) versions >= 4.2.0.Alpha1, <= 4.2.12.Final is affected.
Yes. CVE-2026-42585 is fixed in 4.2.13.Final, 4.1.133.Final. Upgrade to this version or later.
Whether CVE-2026-42585 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
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.
io.netty:netty-codec-http to 4.2.13.Final or laterio.netty:netty-codec-http to 4.1.133.Final or later