CVE-2026-53597 Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader
Attackers can execute arbitrary JavaScript by crafting malicious .prompty files with executable frontmatter, affecting users of the Prompty TypeScript loader.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-53597?
CVE-2026-53597 is a high-severity code injection vulnerability in microsoft prompty, published on 16 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Prompty is a markdown file format (.prompty) for LLM prompts. From 2.0.0-alpha.1 until 2.0.0-beta.3, the @prompty/core TypeScript loader in runtime/typescript/packages/core/src/core/loader.ts used gray-matter without overriding executable js and javascript frontmatter engines, allowing an attacker-controlled .prompty file with ---js frontmatter to execute arbitrary JavaScript during prompt loading. This issue is fixed in version 2.0.0-beta.3.
Weakness: CWE-94
Which versions are affected by CVE-2026-53597?
2 open source packages ship an affected version, including @prompty/core.
| Package | Affected | Fixed in |
|---|---|---|
@prompty/core npm | From 2.0.0-alpha.1 | 2.0.0-beta.3 |
@prompty/core npm | From 2.0.0-alpha.1 | 2.0.0-beta.3 |
How do I fix CVE-2026-53597?
Upgrade @prompty/core to 2.0.0-beta.3 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-53597 being exploited?
There is no known exploitation of CVE-2026-53597 in the wild and no public exploit code.
Sources
Also known as GHSA-c4gh-rv8h-q9vw.