fast-toml through 0.5.4 Prototype Pollution via __proto__ Keys in Parsed TOML

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

12 Oct 2026 20:55:05 UTC

Source modified

26 Oct 2026 17:37:12 UTC

Observed here

26 Oct 2026 18:35:30 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

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CVSS 4.0 · 8.8 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N

CVSS 3.1 · 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L