CVE-2026-53597: Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader

July 17, 2026

The TypeScript Prompty loader used gray-matter without overriding executable frontmatter engines. gray-matter supports JavaScript frontmatter blocks such as ---js and evaluates them while parsing. An attacker-controlled .prompty file could therefore execute arbitrary JavaScript during prompt loading.

References

github.com/advisories/GHSA-c4gh-rv8h-q9vw
github.com/microsoft/prompty/commit/c27402da2487075be577f06aa79df627fb9d6853
github.com/microsoft/prompty/security/advisories/GHSA-c4gh-rv8h-q9vw
nvd.nist.gov/vuln/detail/CVE-2026-53597

Code Behaviors & Features

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