---
id: CVE-2021-48012
title: >-
  fast-toml through 0.5.4 contains a prototype pollution vulnerability that
  allows attackers to modify Object.prototype by supplying TOML containing
  __proto__, constructor or prototype key segments
summary: >-
  fast-toml through 0.5.4 contains a prototype pollution vulnerability that
  allows attackers to modify Object.prototype by supplying TOML containing
  __proto__, constructor or prototype key segments. Attackers can pass
  [__proto__] or [const…
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L'
cwe:
  - CWE-1321
published: '2026-10-12'
updated: '2026-10-12'
sourceUpdated: '2026-10-12T21:17:06.057'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-48012'
references:
  - url: 'https://github.com/Gin-Quin/fast-toml'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/Gin-Quin/fast-toml/issues/8'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/Gin-Quin/fast-toml/pull/3'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/fast-toml-through-0.5.4-prototype-pollution-via-proto-keys-in-parsed-toml
    label: disclosure@vulncheck.com
tags:
  - nvd
ingestedAt: '2026-10-12T22:05:40.350Z'
---

## Overview

fast-toml through 0.5.4 contains a prototype pollution vulnerability that allows attackers to modify Object.prototype by supplying TOML containing __proto__, constructor or prototype key segments. Attackers can pass [__proto__] or [constructor.prototype] table headers or __proto__.x dotted keys to parse() to pollute all objects, causing denial of service or authorization bypass.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.