A critical code injection vulnerability in Microsoft Prompty allows unauthenticated remote attackers to achieve arbitrary code execution on the host system.

The vulnerability stems from improper neutralization of template engine elements within the Nunjucks renderer, which permits unrestricted JavaScript member access. An unauthenticated attacker can supply a malicious template body to traverse object prototypes and execute code within the host Node.js environment.

Successful exploitation grants an attacker full control over the host Node.js process, potentially leading to unauthorized data access, system compromise, or lateral movement within the network. Given the CVSS score of 10.0, this represents a critical risk to infrastructure integrity and confidentiality, as the attack requires no authentication and can be performed remotely.

Immediate Action: Update the npm package @prompty/core to version 0.1.5 or 2.0.0-beta.5 immediately.

Proactive Monitoring: Review application logs for unusual template inputs or unexpected process execution patterns originating from Prompty services.

Compensating Controls: Implement strict input validation for all .prompty files and ensure the Node.js process runs with the least privilege necessary to limit the impact of potential code execution.

Public Exploit Available: Unknown

This vulnerability poses a maximum-severity risk to any environment utilizing the Prompty library. Organizations must prioritize applying the provided updates immediately to prevent potential remote code execution, as the lack of authentication requirements makes this an ideal target for automated exploitation.