MIME header injection via unsanitized multipart names
Published Jul 28, 2026 · Updated Jul 28, 2026
CRLF injection in Netty before 4.1.136.Final and 4.2.0.Final through 4.2.15.Final allows attackers to inject MIME headers. HttpPostRequestEncoder concatenates FileUpload filenames and field names into Content-Disposition lines, while setFilename checks only for null and leaves CRLF delimiters intact. Exploitation requires an application to build multipart requests from attacker-controlled names without independent CRLF filtering; successful injection spoofs content types or overrides form fields.
Summary
What happened
CRLF injection in Netty before 4.1.136.Final and 4.2.0.Final through 4.2.15.Final allows attackers to inject MIME headers. HttpPostRequestEncoder concatenates FileUpload filenames and field names into Content-Disposition lines, while setFilename checks only for null and leaves CRLF delimiters intact. Exploitation requires an application to build multipart requests from attacker-controlled names without independent CRLF filtering; successful injection spoofs content types or overrides form fields.
The record
- CVE
- CVE-2026-59921
- Published
- Jul 28, 2026
- Updated
- Jul 28, 2026
- Vendor
- The Netty Project
- Product
- Netty
- Classifications
- CWE-93
- Attack vector
- adjacent
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 28, 2026CVE publishedPublication date reported by the CVE source.
- Jul 28, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 4.1.136.Final
- Affected versionversion=>=4.2.0.Final, < 4.2.16.Final
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- MultipartFilenameInjectionPoC.javaproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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