Summary
Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader
The TypeScript Prompty loader used gray-matter without overriding executable frontmatter engines. gray-matter supports JavaScript frontmatter blocks such as ---js and evaluates them while parsing. An attacker-controlled .prompty file could therefore execute arbitrary JavaScript during prompt loading.
Affected package
- npm
@prompty/corev2 prerelease line:>= 2.0.0-alpha.1 < 2.0.0-beta.3 - Fixed in
@prompty/[email protected]
The legacy v1 JavaScript runtime had a historical hardening change for this issue. During the v2 TypeScript runtime rebuild, the loader again called gray-matter directly and the vulnerable behavior was present in the v2 prerelease packages until 2.0.0-beta.3.
Fix details
Fixed by commit c27402da2487075be577f06aa79df627fb9d6853 and released via typescript/2.0.0-beta.3.
Impact
Applications that load untrusted .prompty files, user-provided prompt paths, or prompt bundles from less-trusted locations could execute arbitrary JavaScript in the host Node.js process during frontmatter parsing.
Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Upgrade @prompty/core to 2.0.0-beta.3 or later.
The fix explicitly overrides the js and javascript gray-matter engines and rejects JavaScript frontmatter in .prompty files. Prompty frontmatter is YAML-only; executable frontmatter is unsupported. A regression test now verifies that ---js frontmatter is rejected and not evaluated.
Frequently Asked Questions
- What is CVE-2026-53597? CVE-2026-53597 is a high-severity code injection vulnerability in @prompty/core (npm), affecting versions >= 2.0.0-alpha.1, < 2.0.0-beta.3. It is fixed in 2.0.0-beta.3. Untrusted input is evaluated as executable code within the application's runtime environment.
- Which versions of @prompty/core are affected by CVE-2026-53597? @prompty/core (npm) versions >= 2.0.0-alpha.1, < 2.0.0-beta.3 is affected.
- Is there a fix for CVE-2026-53597? Yes. CVE-2026-53597 is fixed in 2.0.0-beta.3. Upgrade to this version or later.
- Is CVE-2026-53597 exploitable, and should I be worried? Whether CVE-2026-53597 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-53597 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-53597? Upgrade
@prompty/coreto 2.0.0-beta.3 or later.