CVE-2026-19484: @fastify/busboy Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-xjh9-v7x6-24jw
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CVSS 7.5
CWE-835 CWE-1322
Published
Advisory Summary

CVE-2026-19484 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')) affecting @fastify/busboy libraries in the npm ecosystem. The issue involves @fastify/busboy vulnerable to denial of service via oversized multipart boundary. Remediation is available by upgrading affected packages to version 3.2.1.

CVE-2026-19484 at a Glance

CVE Identifier CVE-2026-19484
GHSA Identifier GHSA-xjh9-v7x6-24jw
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')
Affected Product @fastify/busboy
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-19484

To remediate this vulnerability, upgrade all affected @fastify/busboy dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

@fastify/busboy fixed: 3.2.1 
npm install @fastify/busboy@3.2.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls @fastify/busboy

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-19484, inspect your project dependencies using npm:

npm ls @fastify/busboy

Analyze the terminal output to locate any version of @fastify/busboy in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.2.1), your application is affected.

Note: The npm ls @fastify/busboy command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop'), where the product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. In @fastify/busboy, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Versions of `@fastify/busboy` from 3.1.0 and prior to 3.2.1 are vulnerable to a Denial of Service. The vendored streaming multipart search stores its default skip distance in a `Uint8Array(256)`. A multipart boundary of exactly 252 bytes makes the search needle 256 bytes, and the table entry wraps to zero, so a crafted request keeps the search in a CPU-bound loop and stalls the Node.js event loop. An unauthenticated client can trigger this with a single small request. Applications that use `@fastify/busboy` to parse multipart/form-data, directly or through `@fastify/multipart`, are affected. ### Patches Fixed in version 3.2.1. ### Workarounds Validate the multipart boundary before parsing and reject any boundary longer than the RFC 2046 limit of 70 characters (for example at a reverse proxy or in an onRequest hook). Upgrading to 3.2.1 removes the issue.

CVE-2026-19484 Affected @fastify/busboy Versions

1 component(s)
Fixed Versions:
3.2.1
Product / Package Ecosystem Affected Versions Fixed Version
@fastify/busboy
npm/@fastify/busboy
npm
≥ 3.1.0
< 3.2.1
3.2.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/fastify/busboy/security/advisories/GHSA-xjh9-v7x6-24jw
NVD — CVE-2026-19484 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-19484
Security Fix Commit FIX COMMIT
https://github.com/fastify/busboy/commit/632a237e7fb6b3b7a30e0de8fab2ee72ca5bf722
@fastify/busboy Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
@fastify/busboy Source Repository REPOSITORY
https://github.com/fastify/busboy
@fastify/busboy Release RELEASE
https://github.com/fastify/busboy/releases/tag/v3.2.1

Frequently Asked Questions

What is CVE-2026-19484?
CVE-2026-19484 is a security vulnerability in @fastify/busboy involving @fastify/busboy vulnerable to Denial of Service via oversized multipart boundary under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop').
Which @fastify/busboy versions are affected?
Affected versions include releases prior to 3.2.1 across affected packages: @fastify/busboy.
What version fixes CVE-2026-19484?
Upgrading to 3.2.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is @fastify/busboy affected?
Yes, @fastify/busboy is affected in releases prior to 3.2.1. Upgrade your dependency to 3.2.1 or later.
What is the CVSS score of CVE-2026-19484?
CVE-2026-19484 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-19484?
CVE-2026-19484 is classified under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop') (The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.).
How can I check npm dependencies for CVE-2026-19484?
Run the dependency tree command: 'npm ls @fastify/busboy'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xjh9-v7x6-24jw",
  "modified" : "2026-10-02T23:16:17Z",
  "published" : "2026-10-02T23:16:17Z",
  "aliases" : [ "CVE-2026-19484" ],
  "summary" : "@fastify/busboy vulnerable to Denial of Service via oversized multipart boundary",
  "details" : "### Impact\n\nVersions of `@fastify/busboy` from 3.1.0 and prior to 3.2.1 are vulnerable to a Denial of Service. The vendored streaming multipart search stores its default skip distance in a `Uint8Array(256)`. A multipart boundary of exactly 252 bytes makes the search needle 256 bytes, and the table entry wraps to zero, so a crafted request keeps the search in a CPU-bound loop and stalls the Node.js event loop. An unauthenticated client can trigger this with a single small request. Applications that use `@fastify/busboy` to parse multipart/form-data, directly or through `@fastify/multipart`, are affected.\n\n### Patches\n\nFixed in version 3.2.1.\n\n### Workarounds\n\nValidate the multipart boundary before parsing and reject any boundary longer than the RFC 2046 limit of 70 characters (for example at a reverse proxy or in an onRequest hook). Upgrading to 3.2.1 removes the issue.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@fastify/busboy"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.1.0"
      }, {
        "fixed" : "3.2.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fastify/busboy/security/advisories/GHSA-xjh9-v7x6-24jw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-19484"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/busboy/commit/632a237e7fb6b3b7a30e0de8fab2ee72ca5bf722"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fastify/busboy"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/busboy/releases/tag/v3.2.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1322", "CWE-835" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-02T23:16:17Z",
    "nvd_published_at" : "2026-08-13T10:17:11Z"
  }
}