Bug 2520904 (CVE-2026-74866)

Summary: CVE-2026-74866 @fastify/busboy: @fastify/busboy: CRLF injection via multipart Content-Disposition filename and name
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, amctagga, aoconnor, aos-team-art-private, asdas, ataylor, bniver, dbruscin, dpaolell, ehugonne, flucifre, gmeno, groman, jdelft, jupierce, kvanderr, lgarciaa, mbenjamin, mbiarnes, mhackett, ppalepu, ppostler, prdhamdh, sghai, sidsharm, sostapov, suppawar, vereddy, vlaad
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in @fastify/busboy, a Node.js multipart form-data parser. The parser incorrectly handles lone carriage return or line feed characters in multipart part headers, treating them as part of the filename or field name rather than as line breaks. A remote attacker could exploit this by uploading a file with a specially crafted filename or field name, leading to control character injection. This could result in filesystem filename pollution, log forging, or header injection in applications that process these values.
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Description OSIDB Bzimport 2026-08-21 08:31:21 UTC 
@fastify/busboy is a multipart form-data parser for Node.js. Its multipart part-header parser splits header lines only on the two-byte carriage-return line-feed sequence, so a lone carriage return or line feed embedded in a part header is not treated as a line break and is carried verbatim into the parsed Content-Disposition filename and field name handed to the application. An attacker who uploads a file whose filename or field name contains a bare carriage return or line feed can inject control characters into consumers that trust the parser to return clean values, enabling filesystem filename pollution, log forging, or header injection when the value is forwarded to a carriage-return-sensitive sink. All versions of @fastify/busboy up to and including 3.2.1 are affected. The issue is fixed in version 3.2.2, which rejects any header line that still contains a bare carriage return or line feed. Users should upgrade to 3.2.2, and consumers such as @fastify/multipart should bump their @fastify/busboy dependency to pull in the fix.