PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-53597 microsoft CVE debrief

CVE-2026-53597 is a high-severity vulnerability in Prompty, a markdown file format for LLM prompts. The vulnerability allows an attacker to execute arbitrary JavaScript during prompt loading due to the @prompty/core TypeScript loader in runtime/typescript/packages/core/src/core/loader.ts using gray-matter without overriding executable js and javascript frontmatter engines. This issue was fixed in version 2.0.0-beta.3. Affected users should review and validate user-controlled .prompty files and implement additional security measures to prevent arbitrary JavaScript execution.

Vendor
microsoft
Product
prompty
CVSS
HIGH 8.7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-16
Original CVE updated
2026-07-16
Advisory published
2026-07-16
Advisory updated
2026-07-16

Who should care

Developers and users of Prompty, especially those using versions between 2.0.0-alpha.1 and 2.0.0-beta.3, should be aware of this vulnerability and take steps to mitigate it. This includes reviewing and validating user-controlled .prompty files and implementing additional security measures to prevent arbitrary JavaScript execution.

Technical summary

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. This allowed an attacker-controlled .prompty file with ---js frontmatter to execute arbitrary JavaScript during prompt loading. The vulnerability was fixed in version 2.0.0-beta.3. Developers and users of Prompty should be aware of this vulnerability and take steps to mitigate it.

Defensive priority

High

Recommended defensive actions

  • Update to version 2.0.0-beta.3 or later
  • Review and validate user-controlled .prompty files
  • Implement additional security measures to prevent arbitrary JavaScript execution
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record was published on 2026-07-16T16:19:12.860Z and last modified on 2026-07-16T17:18:15.407Z. The NVD entry is currently Deferred. There is limited information available about the vulnerability, and defenders should verify the affected scope and severity with the vendor. 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.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-16T16:19:12.860Z and has not been modified since then. The NVD entry is currently Deferred.