HTTP response desynchronization in Netty HttpClientCodec
CVE-2026-42584 is a response desynchronization flaw in Netty's HTTP client handling, affecting netty-codec-http prior to versions 4.2.13.Final and 4.1.133.Final. In HttpClientCodec, inbound responses are paired with outbound requests by calling queue.poll() once per response, including for 1xx informational responses. In an HTTP/1.1 pipelining scenario where a client sends a GET followed by a HEAD request and the server returns a 103 informational response, then a 200 response carrying the GET body, then a 200 response for the HEAD request, the request/response pairing becomes misaligned. The HEAD request can be incorrectly associated with the first 200 response. Because HEAD responses are expected to have no body, the codec skips reading that message body, leaving the GET entity bytes on the stream. Subsequent parsing then occurs from the wrong offset, causing downstream responses to be interpreted incorrectly. The issue is effectively an HTTP message parsing/desynchronization bug on the client connection.
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