Microsoft Prompty up to 0.1.4/2.0.0-beta.4 TypeScript Nunjucks Renderer code injection

Summaryinfo

A vulnerability marked as critical has been reported in Microsoft Prompty up to 0.1.4/2.0.0-beta.4. Impacted is an unknown function of the component TypeScript Nunjucks Renderer. The manipulation leads to code injection. This vulnerability is documented as CVE-2026-73299. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in Microsoft Prompty up to 0.1.4/2.0.0-beta.4. It has been rated as critical. This issue affects an unknown code of the component TypeScript Nunjucks Renderer. The manipulation with an unknown input leads to a code injection vulnerability. Using CWE to declare the problem leads to 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. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-73299 since 08/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/12/2026). MITRE ATT&CK project uses the attack technique T1059 for this issue.

Upgrading to version 0.1.5 or 2.0.0-beta.5 eliminates this vulnerability.

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Productinfo

Vendor

• Microsoft

Name

• Prompty

Version

• 0.1.0
• 0.1.1
• 0.1.2
• 0.1.3
• 0.1.4
• 2.0.0-beta.0
• 2.0.0-beta.1
• 2.0.0-beta.2
• 2.0.0-beta.3
• 2.0.0-beta.4

License

• commercial

Website

• Vendor: https://www.microsoft.com/
• Product: https://github.com/microsoft/prompty/

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