CVE-2026-42581: netty HTTP Request/Response Smuggling

Vulnerability summary

CVE-2026-42581 is a critical (CVSS 9.8) HTTP Request/Response Smuggling vulnerability in netty. EPSS estimates a 0.68% chance of exploitation in the next 30 days, higher than 51.6% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 13-05-2026
   PublishedVulnerability first disclosed.
2. 18-09-2026
   Last modifiedVulnerability information updated.

Description

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpObjectDecoder strips a conflicting Content-Length header when a request carries both Transfer-Encoding: chunked and Content-Length, but only for HTTP/1.1 messages. The guard is absent for HTTP/1.0. An attacker that sends an HTTP/1.0 request with both headers causes Netty to decode the body as chunked while leaving Content-Length intact in the forwarded HttpMessage. Any downstream proxy or handler that trusts Content-Length over Transfer-Encoding will disagree on message boundaries, enabling request smuggling. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

• CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.