CVE-2026-59921
5.7 · MEDIUMOverview
CVE-2026-59921 is a medium-severity vulnerability affecting netty netty. It was published on July 28, 2026 and has a CVSS 3.1 base score of 5.7 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 5.7, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.
Technical 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.
Remediation
Check the references section for vendor advisories and patches from netty. Update netty to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| netty | netty | >= 0, < 4.1.136 | Affected |
Frequently Asked Questions
What is CVE-2026-59921?
CVE-2026-59921 is a medium-severity vulnerability affecting netty netty. It was published on July 28, 2026 and has a CVSS 3.1 base score of 5.7 (MEDIUM).
How severe is CVE-2026-59921?
This vulnerability has a CVSS 3.1 base score of 5.7, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.
How do I fix or remediate CVE-2026-59921?
Check the references section for vendor advisories and patches from netty. Update netty to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-59921?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-59921 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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