Medium severity · published Sep 10, 2026
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
6.5
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 21% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NE
netty · netty
4.1.133.Final before 4.1.138.Final; 4.2.13.Final before 4.2.18.Final · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-89044
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-89044
Product
https://github.com/netty/netty
Product
https://github.com/netty/netty/blob/netty-4.1.137.Final/codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectDecoder.java#L866
Patch
https://github.com/netty/netty/commit/640d4d3324f7b811a4903d0730c8ccb35500500c
Patch
https://github.com/netty/netty/commit/ca87393b0e9e13c493d213a268e727a6d44e1585
Release Notes
https://github.com/netty/netty/releases/tag/netty-4.1.138.Final
Release Notes
https://github.com/netty/netty/releases/tag/netty-4.2.18.Final
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