Netty HttpPostRequestEncoder CRLF Injection <4.1.136 & <4.2.16 Fix
CVE-2026-59921 Published on July 28, 2026
Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder
Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, HttpPostRequestEncoder constructs multipart HTTP request bodies by directly concatenating user-supplied filenames and field names into Content-Disposition MIME headers without validating or sanitizing CRLF characters (\r\n). Since MIME headers are delimited by CRLF, an attacker who controls the filename can inject arbitrary MIME headers into the multipart body part. The root cause is that neither the encoder nor the FileUpload implementations' setFilename() methods, which only check for null, neutralize CRLF characters before the filename is embedded into the header. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.
Vulnerability Analysis
Weakness Type
What is a CRLF Injection Vulnerability?
The software uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.
CVE-2026-59921 has been classified to as a CRLF Injection vulnerability or weakness.
Products Associated with CVE-2026-59921
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Affected Versions
netty:- Version >=4.2.0.Final, < 4.2.16.Final is affected.
- Version < 4.1.136.Final is affected.