Header injection via preserved multipart CRLF
Published Apr 2, 2026 · Updated Apr 2, 2026
CRLF injection in Rack 3.2.0 through 3.2.5 allows remote attackers to alter downstream HTTP response headers via multipart uploads. Rack::Multipart::Parser accepts obs-fold in Content-Disposition and Content-Type, then retains the embedded CRLF in filename, name, and type values instead of replacing the fold with whitespace. Exploitation requires an application to accept the crafted multipart request and reuse the parsed metadata in a header-sensitive context, enabling header injection or response splitting without reported availability impact.
Summary
What happened
CRLF injection in Rack 3.2.0 through 3.2.5 allows remote attackers to alter downstream HTTP response headers via multipart uploads. Rack::Multipart::Parser accepts obs-fold in Content-Disposition and Content-Type, then retains the embedded CRLF in filename, name, and type values instead of replacing the fold with whitespace. Exploitation requires an application to accept the crafted multipart request and reuse the parsed metadata in a header-sensitive context, enabling header injection or response splitting without reported availability impact.
The record
- CVE
- CVE-2026-26962
- Published
- Apr 2, 2026
- Updated
- Apr 2, 2026
- Vendor
- Rack
- Product
- Rack
- Classifications
- CWE-93, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 2, 2026CVE publishedPublication date reported by the CVE source.
- Apr 2, 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=>= 3.2.0, < 3.2.6
What conditions does exploitation require?
What is affected?
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
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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