CVE-2026-89044: netty HTTP Request/Response Smuggling

Vulnerability summary

CVE-2026-89044 is a medium (CVSS 6.9) HTTP Request/Response Smuggling vulnerability in netty. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 19.6% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 10-09-2026
   PublishedVulnerability first disclosed.
2. 18-09-2026
   Last modifiedVulnerability information updated.

Description

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.

• 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.