Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader

## Summary 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. ## Affected package - npm `@prompty/core` v2 prerelease line: `>= 2.0.0-alpha.1 < 2.0.0-beta.3` - Fixed in `@prompty/core@2.0.0-beta.3` The legacy v1 JavaScript runtime had a historical hardening change for this issue. During the v2 TypeScript runtime rebuild, the loader again called `gray-matter` directly and the vulnerable behavior was present in the v2 prerelease packages until `2.0.0-beta.3`. ## Impact Applications that load untrusted `.prompty` files, user-provided prompt paths, or prompt bundles from less-trusted locations could execute arbitrary JavaScript in the host Node.js process during frontmatter parsing. ## Remediation Upgrade `@prompty/core` to `2.0.0-beta.3` or later. The fix explicitly overrides the `js` and `javascript` gray-matter engines and rejects JavaScript frontmatter in `.prompty` files. Prompty frontmatter is YAML-only; executable frontmatter is unsupported. A regression test now verifies that `---js` frontmatter is rejected and not evaluated. ## Fix details Fixed by commit `c27402da2487075be577f06aa79df627fb9d6853` and released via `typescript/2.0.0-beta.3`. Source Code Location: https://github.com/microsoft/prompty Affected Packages: - npm:@prompty/core, affected >= 2.0.0-alpha.1, < 2.0.0-beta.3, patched in 2.0.0-beta.3 CWEs: - CWE-94: Improper Control of Generation of Code ('Code Injection') CVSS: - CVSS_V4: score 8.7, CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N References: - https://github.com/microsoft/prompty/security/advisories/GHSA-c4gh-rv8h-q9vw - https://nvd.nist.gov/vuln/detail/CVE-2026-53597 - https://github.com/microsoft/prompty/commit/c27402da2487075be577f06aa79df627fb9d6853 - https://github.com/advisories/GHSA-c4gh-rv8h-q9vw