CVE-2026-73299
Received Received - Intake

Prototype Pollution in Prompty Template Engine

Publication date: 2026-08-12

Last updated on: 2026-08-12

Assigner: GitHub, Inc.

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.

CVSS Scores

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Meta Information

Published
2026-08-12
Last Modified
2026-08-12
Generated
2026-08-13
AI Q&A
2026-08-12
EPSS Evaluated
N/A
NVD
CVE-2026-73299
EUVD
EUVD-2026-57382

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
microsoft prompty 0.1.5
microsoft prompty to 2.0.0-beta.5 (inc)

Helpful Resources

Exploitability

CWE
CWE Icon
KEV
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CWE ID Description
CWE-94 The product 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.
CWE-1336 The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine.

Attack-Flow Graph

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Executive Summary

This vulnerability is a Server-Side Template Injection (SSTI) in the Prompty library's Nunjucks template renderer. It allows attackers to execute arbitrary JavaScript in the host Node.js process by injecting malicious template code. The issue stems from unrestricted JavaScript member access in .prompty template files, enabling prototype traversal and code execution through properties like __proto__, constructor, and prototype.

Detection Guidance

Detecting this vulnerability requires checking if your system uses vulnerable versions of Prompty (before 0.1.5 or 2.0.0-beta.5). Inspect installed packages with commands like 'npm list @prompty/core' or 'pip show prompty'. If vulnerable versions are found, update immediately. No direct network detection commands are provided in the context.

Impact Analysis

If you use Prompty versions before 0.1.5 or 2.0.0-beta.5, an attacker could craft a malicious .prompty file that executes arbitrary code on your server when processed. This could lead to complete system compromise, data theft, or further network infiltration. The high CVSS score (10.0) indicates maximum impact across confidentiality, integrity, and availability.

Compliance Impact

This vulnerability could lead to unauthorized data access or modification, violating GDPR's data protection requirements and HIPAA's security rules for protected health information. A successful exploit might result in data breaches that trigger mandatory breach notifications and regulatory fines under these standards.

Mitigation Strategies

Immediately upgrade Prompty to versions 0.1.5 or 2.0.0-beta.5 or later. Remove or restrict access to any untrusted .prompty files. Review template files for suspicious content that might exploit prototype pollution or code injection. Monitor for unusual system behavior.

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