{"id":"CVE-2026-53597","aliases":["EUVD-2026-44939","GHSA-c4gh-rv8h-q9vw"],"status":"published","title":"Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader","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.","severity":{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00972,"percentile":0.62391,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-94"],"published":"2026-07-16T14:54:55Z","modified":"2026-10-28T02:30:44Z","fixes":[{"ecosystem":"npm","package":"@prompty/core","fixed_in":["2.0.0-beta.3"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"@prompty/core","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0-alpha.1"},{"fixed":"2.0.0-beta.3"}]}]},{"source":"osv","ecosystem":"npm","package":"@prompty/core","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0-alpha.1"},{"fixed":"2.0.0-beta.3"}]}]}],"products":[{"vendor":"microsoft","product":"prompty"}],"references":[{"url":"https://github.com/microsoft/prompty/security/advisories/GHSA-c4gh-rv8h-q9vw","tags":["x_refsource_CONFIRM","advisory","web"]},{"url":"https://github.com/microsoft/prompty/commit/c27402da2487075be577f06aa79df627fb9d6853","tags":["x_refsource_MISC","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-53597","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-c4gh-rv8h-q9vw"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53597.json","tags":["advisory"]},{"url":"https://github.com/microsoft/prompty","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-53597","title":"Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader","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.","status":"published","published":"2026-07-16T14:54:55.075Z","modified":"2026-07-18T02:51:03.9Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","level":"high","assessor":"cna"}],"cwes":["CWE-94"],"updated_at":"2026-11-02T14:20:00.11477Z"}],"euvd":[{"id":"EUVD-2026-44939","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.","status":"published","published":"2026-07-16T14:54:55Z","modified":"2026-07-18T02:51:03Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","level":"high"}],"updated_at":"2026-11-02T18:19:50.065723Z"}],"ghsa":[{"id":"GHSA-c4gh-rv8h-q9vw","title":"Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader","description":"## Summary\nThe 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.\n\n## Affected package\n- npm `@prompty/core` v2 prerelease line: `\u003e= 2.0.0-alpha.1 \u003c 2.0.0-beta.3`\n- Fixed in `@prompty/core@2.0.0-beta.3`\n\nThe 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`.\n\n## Impact\nApplications 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.\n\n## Remediation\nUpgrade `@prompty/core` to `2.0.0-beta.3` or later.\n\nThe 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.\n\n## Fix details\nFixed by commit `c27402da2487075be577f06aa79df627fb9d6853` and released via `typescript/2.0.0-beta.3`.","status":"published","published":"2026-07-17T19:53:34Z","modified":"2026-07-17T19:53:37Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","level":"high"}],"cwes":["CWE-94"],"updated_at":"2026-11-02T14:40:46.257074Z"}],"nvd":[{"id":"CVE-2026-53597","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.","status":"published","published":"2026-07-16T16:19:12.86Z","modified":"2026-10-24T20:10:00.137Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"high","assessor":"secondary"}],"cwes":["CWE-94"],"updated_at":"2026-11-02T14:12:30.250437Z"}],"osv":[{"id":"CVE-2026-53597","title":"Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader","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.","status":"published","published":"2026-07-16T14:54:55.075Z","modified":"2026-10-28T02:30:44.322152634Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","level":"high"}],"cwes":["CWE-94"],"updated_at":"2026-11-02T15:45:08.132336Z"},{"id":"GHSA-c4gh-rv8h-q9vw","title":"Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader","description":"## Summary\nThe 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.\n\n## Affected package\n- npm `@prompty/core` v2 prerelease line: `\u003e= 2.0.0-alpha.1 \u003c 2.0.0-beta.3`\n- Fixed in `@prompty/core@2.0.0-beta.3`\n\nThe 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`.\n\n## Impact\nApplications 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.\n\n## Remediation\nUpgrade `@prompty/core` to `2.0.0-beta.3` or later.\n\nThe 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.\n\n## Fix details\nFixed by commit `c27402da2487075be577f06aa79df627fb9d6853` and released via `typescript/2.0.0-beta.3`.","status":"published","published":"2026-07-17T19:53:34Z","modified":"2026-07-17T20:00:17.099953006Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","level":"high"}],"cwes":["CWE-94"],"updated_at":"2026-11-02T15:46:44.571161Z"}]}}