---
id: CVE-2026-73299
title: Prompty is a markdown file format (.prompty) for LLM prompts
summary: >-
  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-controll…
severity: critical
cvss: 10
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H'
cwe:
  - CWE-94
  - CWE-1336
vendor: microsoft
product: prompty
affected:
  - prompty < 0.1.5
  - 'prompty >= 2.0.0-alpha.1, < 2.0.0-beta.5'
published: '2026-08-12'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T21:02:22.660'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-73299'
references:
  - url: >-
      https://github.com/microsoft/prompty/commit/e4a0ebf49e3a78d5d7796c8480bf9a4f0c54d19e
    label: security-advisories@github.com
  - url: >-
      https://github.com/microsoft/prompty/commit/f5c57c94a0990cca79d095c3daab661b4b1fb89f
    label: security-advisories@github.com
  - url: 'https://github.com/microsoft/prompty/pull/404'
    label: security-advisories@github.com
  - url: 'https://github.com/microsoft/prompty/pull/405'
    label: security-advisories@github.com
  - url: >-
      https://github.com/microsoft/prompty/security/advisories/GHSA-w28w-gp39-m4p6
    label: security-advisories@github.com
  - url: 'https://github.com/microsoft/prompty/tree/typescript/2.0.0-beta.5'
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-08-12T18:53:50.277151Z'
ingestedAt: '2026-09-14T12:29:35.090Z'
epss: 0.01784
epssPercentile: 0.77324
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.