HTTP Request Smuggling Affecting io.netty:netty-codec-http package, versions [,4.1.133.Final)[4.2.0.Alpha1,4.2.13.Final)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JAVA-IONETTY-16438934
- published7 May 2026
- disclosed7 May 2026
- creditsubbudvk
Introduced: 7 May 2026
CVE-2026-42581 (opens in a new tab)How to fix?
Upgrade io.netty:netty-codec-http to version 4.1.133.Final, 4.2.13.Final or higher.
Overview
io.netty:netty-codec-http is a network application framework for rapid development of maintainable high performance protocol servers & clients.
Affected versions of this package are vulnerable to HTTP Request Smuggling in the HttpObjectDecoder component. An attacker can manipulate downstream request interpretation by sending specially crafted HTTP/1.0 requests containing both Transfer-Encoding: chunked and Content-Length headers. This can result in unauthorized access, cache poisoning, or bypassing security controls by causing downstream proxies or handlers to misinterpret message boundaries.
Note:
This is only exploitable if the deployment is behind a reverse proxy or load balancer that prioritizes the Content-Length header, the attacker can send HTTP/1.0 requests, and there is no additional HTTP/1.0 stripping layer between the attacker and the application.