Aug 2026: Prompty: Server-Side Template Injection to Remote Code Execution in the @prompty/core Nunj
CVE-2026-73299 Published on August 12, 2026
Prompty: Server-Side Template Injection to Remote Code Execution in the @prompty/core Nunjucks Renderer
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.
Vulnerability Analysis
CVE-2026-73299 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to be critical as this vulnerability has a high impact to the confidentiality, integrity and availability of this component.
Weakness Types
What is a Code Injection Vulnerability?
The software constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
CVE-2026-73299 has been classified to as a Code Injection vulnerability or weakness.
Affected Versions
microsoft prompty:- Version < 0.1.5 is affected.
- Version >= 2.0.0-alpha.1, < 2.0.0-beta.5 is affected.