CVE-2026-74866: fastify fastify\/busyboy CRLF Injection

Vulnerability summary

CVE-2026-74866 is a medium (CVSS 5.8) CRLF Injection vulnerability in fastify fastify\/busyboy. EPSS estimates a 0.33% chance of exploitation in the next 30 days, higher than 24.2% of scored vulnerabilities.

Timeline

1. 21-08-2026
   PublishedVulnerability first disclosed.
2. 21-08-2026
   Last modifiedVulnerability information updated.

Description

@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.

• CWE-93Improper Neutralization of CRLF Sequences ('CRLF Injection')The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.