Prompty: Server-Side Template Injection to Remote Code Execution in the @prompty/core Nunjucks Renderer

## Summary The TypeScript Nunjucks renderer evaluated untrusted `.prompty` template bodies with unrestricted JavaScript member access. An attacker-controlled template could traverse constructor and prototype properties to execute JavaScript in the host Node.js process. ## Affected packages - npm `@prompty/core` versions `<= 0.1.4` - npm `@prompty/core` versions `<= 2.0.0-beta.4` ## Impact Applications that render untrusted, community-supplied, cloned, or LLM-generated `.prompty` files with the TypeScript runtime could allow attacker-controlled code execution with the privileges of the Node.js host process. ## Remediation Upgrade to `@prompty/core` `2.0.0-beta.5` or later. The patched renderer sanitizes render inputs to own-data-only values, rejects constructor/prototype member traversal, and disallows template function calls. Ordinary interpolation, conditionals, loops, and own nested data properties remain supported. ## Fix details The fix is merged in PR #404 and includes regression coverage for default Nunjucks rendering, explicit renderer usage, unsafe member lookups, and attempted template function calls.

Source published

24 Jul 2026 16:23:59 UTC

Source modified

13 Aug 2026 04:11:08 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_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Publisher rating · CRITICAL