Netty prior 4.1.136.Final/4.2.16.Final HttpPostRequestEncoder setFilename crlf injection

Summaryinfo

A vulnerability has been found in Netty and classified as problematic. Impacted is the function setFilename of the component HttpPostRequestEncoder. This manipulation causes crlf injection. This vulnerability is tracked as CVE-2026-59921. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Netty. It has been declared as problematic. Affected by this vulnerability is the function setFilename of the component HttpPostRequestEncoder. The manipulation with an unknown input leads to a crlf injection vulnerability. The CWE definition for the vulnerability is CWE-93. The product 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. As an impact it is known to affect integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-59921 since 07/07/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details are known, but no exploit is available.

Upgrading to version 4.1.136.Final or 4.2.16.Final eliminates this vulnerability.

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Productinfo

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• Netty

Website

• Product: https://github.com/netty/netty/

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