CVE-2026-42585: Netty: HTTP Request Smuggling due to malformed Transfer-Encoding

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-13 · updated 2026-10-26
Weakness: CWE-444

Description

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty incorrectly parses malformed Transfer-Encoding, enabling request smuggling attacks. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Affected products

netty: before 4.1.133; from 4.2.0 before 4.2.13 — fixed in 4.1.133, 4.2.13

How to fix

Upgrade to a fixed version: netty 4.1.133, 4.2.13. Check the vendor advisory for mitigations.

References

https://github.com/netty/netty/security/advisories/GHSA-38f8-5428-x5cv
https://github.com/netty/netty/security/advisories/GHSA-38f8-5428-x5cv

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