CVE-2025-58056: Netty is vulnerable to request smuggling due to incorrect parsing of chunk extensions

Vulnerability summary

CVE-2025-58056 is a high (CVSS 7.5) vulnerability in netty. EPSS estimates a 0.71% chance of exploitation in the next 30 days, higher than 53.5% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 03-09-2025
   PublishedVulnerability first disclosed.
2. 05-09-2025
   Last modifiedVulnerability information updated.

Description

Netty is an asynchronous event-driven network application framework for development of maintainable high performance protocol servers and clients. In versions 4.1.124.Final, and 4.2.0.Alpha3 through 4.2.4.Final, Netty incorrectly accepts standalone newline characters (LF) as a chunk-size line terminator, regardless of a preceding carriage return (CR), instead of requiring CRLF per HTTP/1.1 standards. When combined with reverse proxies that parse LF differently (treating it as part of the chunk extension), attackers can craft requests that the proxy sees as one request but Netty processes as two, enabling request smuggling attacks. This is fixed in versions 4.1.125.Final and 4.2.5.Final.

• CWE-444Inconsistent Interpretation of HTTP RequestsThe 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.