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10.0

Prompty: Malicious Markdown Can Run Unwanted Code

CVE-2026-73299 · published 22 days ago
Summary

A security issue in Prompty, a markdown file format for LLM prompts, allowed an attacker to run malicious code on the server. This could potentially lead to unauthorized actions or data breaches. To fix this issue, update to Prompty version 0.1.5 or 2.0.0-beta.5 or later.

What to do

The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.

Affected software
VendorProductAffected versions
microsoft prompty < 0.1.5
Original advisory text
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 JavaSc...
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.
References
Severity
10.0 Critical
CVSS 3.1: 10.0 (MITRE)
Exploitation
EPSS 1%
Type
CWE-94Code Injection
CWE-1336Improper Neutralization of Special Elements Used in a Template Engine
Timeline
Published12 Aug 2026
Updated30 Aug 2026
First seen12 Aug 2026
Sources
CVE-2026-73299 · NVD
CVE-2026-73299 · MITRE
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