CVE-2026-74866 @fastify/busboy vulnerable to CRLF injection via multipart Content-Disposition filename and name
Attackers can inject control characters into parsed filenames or field names, potentially causing log forging or header injection in downstream applications.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74866?
CVE-2026-74866 is a medium-severity vulnerability in @fastify/busboy, published on 21 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-93
Which versions are affected by CVE-2026-74866?
2 open source packages ship an affected version, including @fastify/busboy. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
@fastify/busboy npm | All versions | 3.2.2 |
@fastify/busboy npm | All versions | 3.2.2 |
Products include Fastify Fastify\/Busyboy.
How do I fix CVE-2026-74866?
Upgrade @fastify/busboy to 3.2.2 or later.
Is CVE-2026-74866 being exploited?
There is no known exploitation of CVE-2026-74866 in the wild and no public exploit code.
Other vulnerabilities in @fastify/busboy
Sources
Also known as GHSA-gxm5-99cw-xjw9, MINI-g5g2-45hr-3w83.