What’s Vulnerable › Vulnerabilities

CVE-2026-89044: Netty 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final HTTP Request Smuggling via Transfer-Encoding

• Severity: medium (CVSS 6.5 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: 2026-09-10 · updated 2026-09-18
• Weakness: CWE-444

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.

Affected products

• netty: from 4.1.133 before 4.1.138; from 4.2.13 before 4.2.18 — fixed in 4.1.138, 4.2.18

How to fix

Upgrade to a fixed version: netty 4.1.138, 4.2.18. Check the vendor advisory for mitigations.

References

• https://github.com/netty/netty
• https://github.com/netty/netty/blob/netty-4.1.137.Final/codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectDecoder.java#L866
• https://github.com/netty/netty/commit/640d4d3324f7b811a4903d0730c8ccb35500500c
• https://github.com/netty/netty/commit/ca87393b0e9e13c493d213a268e727a6d44e1585
• https://github.com/netty/netty/releases/tag/netty-4.1.138.Final
• https://github.com/netty/netty/releases/tag/netty-4.2.18.Final
• https://github.com/netty/netty/security/advisories/GHSA-hcvj-94mj-jp5c
• https://www.vulncheck.com/advisories/netty-4.1.133-final-through-4.1.137-final-and-4.2.13-final-through-4.2.17-final-http-request-smuggling-via-transfer-encoding

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