Vulnerability · Published Oct 12, 2026 · Assigned by VulnCheck

CVE-2021-48012fast-toml through 0.5.4 Prototype Pollution via proto Keys in Parsed TOML

High 8.2

In plain English

A high-severity prototype pollution in fast-toml from Gin-Quin. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities).

Severity (CVSS 3.1)8.2High

Exploit odds (30 days)0.4%top 64.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected products (as reported)

Vendor	Product	Versions
Gin-Quin	fast-toml	0 – through 0.5.4

Weakness: CWE-1321 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L

References

GitHub Issue #8 issue-tracking
GitHub Pull Request #3 issue-tracking, patch
https://github.com/Gin-Quin/fast-toml product
VulnCheck Advisory: fast-toml through 0.5.4 Prototype Pollution via __proto__ Keys in Parsed TOML third-party-advisory