---
id: "GHSA-hpvc-wj3g-h9p8"
page: "https://infrastack.ai/live/GHSA-hpvc-wj3g-h9p8"
kind: "vulnerability"
aliases: ["GHSA-hpvc-wj3g-h9p8"]
title: "Blocked event loop via sparse array field names on the Fastify adapter"
severity: "high"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "@nestjs/platform-fastify", "fixed": ["12.1.3"], "affected": ">= 12.1.0, < 12.1.3", "ecosystem": "npm"}]
ecosystems: ["npm"]
tags: ["cwe-400", "cwe-834", "fastify", "nestjs", "node", "package", "self-hosted"]
not_affected_if: ["express-adapter", "no-multipart-uploads"]
published_at: "2026-11-12T19:03:58+00:00"
first_seen_at: "2026-11-12T19:14:24+00:00"
updated_at: "2026-11-12T19:15:44+00:00"
sources: [{"source": "ghsa-repo", "url": "https://github.com/nestjs/nest/security/advisories/GHSA-hpvc-wj3g-h9p8", "first_seen_at": "2026-11-12T19:14:24+00:00"}]
exploit_sources: []
---

# Blocked event loop via sparse array field names on the Fastify adapter

Link for people: https://infrastack.ai/live/GHSA-hpvc-wj3g-h9p8 (this .md is for agents)

A single small multipart request with a large array index in a field name makes @nestjs/platform-fastify spend time proportional to that index, blocking the Node.js event loop. Some field names also make the request fail with a 500 error.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- npm:@nestjs/platform-fastify affected >= 12.1.0, < 12.1.3 fixed 12.1.3

## How to check

- Run `npm ls @nestjs/platform-fastify` to see the installed version.
- Check whether any route uses an upload interceptor from `@nestjs/platform-fastify/multipart`.

## Timeline

- 2026-11-12T19:14:24+00:00 ghsa-repo https://github.com/nestjs/nest/security/advisories/GHSA-hpvc-wj3g-h9p8

## Documents

- [advisory] Maintainer's advisory: github.com https://github.com/nestjs/nest/security/advisories/GHSA-hpvc-wj3g-h9p8

## From the sources

| Field | Value |
| --- | --- |
| Ecosystem | npm |
| Package | `@nestjs/platform-fastify` |
| Affected versions | `>= 12.1.0, < 12.1.3` |
| Patched versions | `12.1.3` |
| Severity | High |
| CVSS v3.1 | `AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` (7.5) |
| CWE | CWE-834 (Excessive Iteration), CWE-400 (Uncontrolled Resource Consumption) |

### Summary

The multipart parser of `@nestjs/platform-fastify` could take time proportional to the largest array index in a field name, not to the number of fields sent. A single small request could block the event loop for a long time, and some field names made the request fail with a 500.

### Impact

Applications using the Fastify adapter with any upload interceptor from `@nestjs/platform-fastify/multipart` are affected. No authentication is needed unless a guard protects the route.

### Patches

Fixed in **12.1.3**. Field objects are built from the items present only, and invalid field names are answered with 400. Since 12.2.0, `fieldArrayIndexLimit` also defaults to 1000.

### Workarounds

Upgrade. There is no configuration workaround on the affected versions.

### Credit

Found by the NestJS maintainers.

---

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