What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-12 · updated 2026-10-26
• Weakness: CWE-1321

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

• Gin-Quin fast-toml: through 0.5.4

References

• https://github.com/Gin-Quin/fast-toml
• https://github.com/Gin-Quin/fast-toml/issues/8
• https://github.com/Gin-Quin/fast-toml/pull/3
• https://www.vulncheck.com/advisories/fast-toml-through-0.5.4-prototype-pollution-via-proto-keys-in-parsed-toml

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