# 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.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Aug 2026
- **Updated:** 21 Aug 2026
- **Also known as:** GHSA-gxm5-99cw-xjw9, MINI-g5g2-45hr-3w83

## 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 (Improper Neutralization of CRLF Sequences)

## Which versions are affected by CVE-2026-74866?

2 open source packages ship an affected version, including @fastify/busboy. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@fastify/busboy` | npm | All versions | 3.2.2 |
| `@fastify/busboy` | npm | All versions | 3.2.2 |

Products: 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

- [CVE-2026-19481](https://insights.sbomify.com/CVE-2026-19481/): @fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header (high 7.5)
- [CVE-2026-19484](https://insights.sbomify.com/CVE-2026-19484/): @fastify/busboy vulnerable to Denial of Service via oversized multipart boundary (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74866 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-74866 in the wild and no public exploit code.

Affected packages and fixed versions:
- @fastify/busboy (npm): affected all versions; fixed in 3.2.2
- @fastify/busboy (npm): affected all versions; fixed in 3.2.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74866/ (Markdown: https://insights.sbomify.com/CVE-2026-74866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74866
- OSV: https://osv.dev/vulnerability/CVE-2026-74866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74866/
Summaries are generated and may contain mistakes; the official description above is the record.