Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader
Exact source revision recorded 24 Oct 2026 13:17:17 UTC. It does not establish the source's current position. Latest evidence.
osv · GHSA-c4gh-rv8h-q9vw
Published## 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/[email protected]` 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 published
- 17 Jul 2026 19:53:34 UTC
- Source modified
- 17 Jul 2026 20:00:17 UTC
- Observed here
- 24 Oct 2026 13:17:17 UTC
- Source terms
- GitHub Advisory Database · CC-BY-4.0
Original source record · Cite this exact observation · Complete original publisher JSON
This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.
CVSS_V4 · 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
Publisher rating · HIGH