RCE in Microsoft Prompty

CVE-2026-73299

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 class: RCE (Remote Code Execution)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.018 (77.4th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 77th percentile — 77.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-73299: rose from 0.012 to 0.018.

EPSS over last 30 days · oldest: 0.012 · newest: 0.018 · change: +0.006

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-73299?
CVE-2026-73299 is a critical-severity vulnerability in Microsoft Prompty, classified under Code Injection. CVSS score: 10.0/10. Published 2026-08-12.
How severe is CVE-2026-73299?
Critical severity. CVSS v3 base score is 10.0 out of 10.