CVE-2026-59921

5.7 MEDIUM 0.5% exploit odds Fix listed Other Device

What it 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.

At a glance

Exploitability: Can be exploited from the same network segment with a low-privilege account. High risk of data tampering.
Exploit odds: 0.5% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-07-28 23:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-08-07 15:05 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.5% in the next 30 days (EPSS).
Severity: 5.7 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-07-28 23:17 UTC
Last modified: 2026-08-07 15:05 UTC
Exploit probability: 0.5% · EPSS, next 30 days
Weakness: CWE-93
Record status: Analyzed

Affected

Netty < 4.1.136
Netty < 4.2.16

Attack profile CVSS 3.1 · 5.7

Attack vector: Adjacent network
Complexity: Low
Privileges needed: Low
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Raw vector

CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-59921.md and follow it. Check whether this project is affected by CVE-2026-59921. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record