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CVE-2026-59921

5.7 · MEDIUM

Netty is an asynchronous, event-driven network application framework.

Published Jul 28, 2026CWE-93EPSS 0.46%

Overview

CVE-2026-59921 is a medium-severity vulnerability. 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, patches, and mitigation guidance. 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.

References

GitHubgithub.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7gGitHubgithub.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g

How CyberStrike helps

Frequently asked questions

What is CVE-2026-59921?

CVE-2026-59921 is a medium-severity vulnerability. 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, patches, and mitigation guidance. 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 is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-59921 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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