Vulnerability Description
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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Netty | Netty | < 4.1.136 |
Related Weaknesses (CWE)
References
- https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7gMitigationVendor Advisory
- https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7gMitigationVendor Advisory
FAQ
What is CVE-2026-59921?
CVE-2026-59921 is a vulnerability with a CVSS score of 5.7 (MEDIUM). 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 conc...
How severe is CVE-2026-59921?
CVE-2026-59921 has been rated MEDIUM with a CVSS base score of 5.7/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-59921?
Check the references section above for vendor advisories and patch information. Affected products include: Netty Netty.