HTTP Request Smuggling Affecting io.netty:netty-codec-http2 package, versions [,4.1.136.Final)[4.2.0.Final,4.2.16.Final)
Threat Intelligence
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-18233111
- published23 Jul 2026
- disclosed22 Jul 2026
- creditUnknown
Introduced: 22 Jul 2026
NewCVE-2026-59900 (opens in a new tab)How to fix?
Upgrade io.netty:netty-codec-http2 to version 4.1.136.Final, 4.2.16.Final or higher.
Overview
io.netty:netty-codec-http2 is a HTTP2 sub package for the netty library, an event-driven asynchronous network application framework.
Affected versions of this package are vulnerable to HTTP Request Smuggling in the translation from HTTP/2 to HTTP/1.x, specifically when handling both the :authority pseudo-header and a literal host header in a single HEADERS frame. An attacker can manipulate request routing by supplying differing values for these headers, resulting in two Host headers in the resulting request object.