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

Severity: high (CVSS 8.7 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-16 · updated 2026-10-24
Weakness: CWE-94

Description

Prompty is a markdown file format (.prompty) for LLM prompts. From 2.0.0-alpha.1 until 2.0.0-beta.3, the @prompty/core TypeScript loader in runtime/typescript/packages/core/src/core/loader.ts used gray-matter without overriding executable js and javascript frontmatter engines, allowing an attacker-controlled .prompty file with ---js frontmatter to execute arbitrary JavaScript during prompt loading. This issue is fixed in version 2.0.0-beta.3.

Affected products

microsoft prompty: from 2.0.0-alpha.1, < 2.0.0-beta.3

References

https://github.com/microsoft/prompty/commit/c27402da2487075be577f06aa79df627fb9d6853
https://github.com/microsoft/prompty/security/advisories/GHSA-c4gh-rv8h-q9vw

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