Prompty is a markdown file format (.prompty) for LLM prompts. Prior to 0.1.5 and 2.0.0-beta.5, 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. This issue is fixed in versions 0.1.5 and 2.0.0-beta.5.

Affected: npm: @prompty/core

## 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.