CVE-2026-89044: Netty

Medium severity, CVSS 6.5. EPSS: 0.3% chance of exploitation in the next 30 days.

Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final fail to properly validate the final transfer coding in the Transfer-Encoding header, allowing attackers to smuggle requests by using malformed encoding declarations. Attackers can split Transfer-Encoding headers across multiple lines or use values like 'chunked, xchunked' to bypass validation and decode messages as chunked when the final coding is not chunked, enabling request smuggling attacks.

Affected products

• Netty Netty: from 4.1.133, before 4.1.138 (fixed in 4.1.138); from 4.2.13, before 4.2.18 (fixed in 4.2.18)

Published 2026-09-10. Last modified 2026-09-18.