HTTP Request Smuggling Affecting io.netty:netty-codec-http package, versions [,4.1.137.Final)[4.2.0.Final,4.2.17.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-20154836
- published27 Sept 2026
- disclosed26 Sept 2026
- creditVioleta Georgieva
Introduced: 26 Sep 2026
NewCVE-2026-100666 (opens in a new tab)How to fix?
Upgrade io.netty:netty-codec-http to version 4.1.137.Final, 4.2.17.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 isContentAlwaysEmpty() method of HttpServerCodec, which calls pollMethod() once per outbound response including for 1xx status codes, so the queue of pending request methods falls out of step with the responses being written. An attacker can have a response body misrouted or dropped and leave the socket unsafe for further pipelined reuse, reaching response smuggling, by pipelining a GET followed by a HEAD while sending Expect: 100-continue, which makes the codec pair the HEAD with the 200 OK intended for the GET, drop that body under HEAD semantics, and then write the HEAD response with a body. This requires HTTP/1.1 pipelining on the connection, a HEAD request following a GET, and the client supplying the Expect: 100-continue header.