What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2025-09-03 · updated 2026-10-19
• Weakness: CWE-444

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.

Affected products

• netty: before 4.1.125; from 4.2.0 before 4.2.5 — fixed in 4.1.125, 4.2.5

How to fix

Upgrade to a fixed version: netty 4.1.125, 4.2.5. Check the vendor advisory for mitigations.

References

• https://datatracker.ietf.org/doc/html/rfc9112#name-chunked-transfer-coding
• https://github.com/JLLeitschuh/unCVEed/issues/1
• https://github.com/netty/netty/commit/edb55fd8e0a3bcbd85881e423464f585183d1284
• https://github.com/netty/netty/issues/15522
• https://github.com/netty/netty/pull/15611
• https://github.com/netty/netty/security/advisories/GHSA-fghv-69vj-qj49
• https://w4ke.info/2025/06/18/funky-chunks.html

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