Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader

{
  "id": "3b547bc1e10be027389c51718804ce65e101fa5f4ce81ffbf674b0fea3c63560",
  "url": "https://osv.dev/vulnerability/CVE-2026-53597",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Prompty: Arbitrary code execution via JavaScript frontmatter in TypeScript loader",
    "summary": "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.",
    "evidence": "osv:CVE-2026-53597",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-53597",
      "aliases": [
        "CVE-2026-53597",
        "GHSA-c4gh-rv8h-q9vw"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/microsoft/prompty",
              "type": "GIT",
              "events": [
                {
                  "introduced": "30acb714bf68259760916c97b0c8fdaf1c5a75a0"
                },
                {
                  "fixed": "c27402da2487075be577f06aa79df627fb9d6853"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "2.0.0-alpha.1"
                      },
                      {
                        "fixed": "2.0.0-beta.3"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "c27402da2487075be577f06aa79df627fb9d6853"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.0.0-beta.3"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "versions": [
            "python/2.0.0b2",
            "typescript/2.0.0-beta.2",
            "rust/2.0.0-beta.2",
            "csharp/2.0.0-beta.2",
            "python/2.0.0b1",
            "typescript/2.0.0-beta.1",
            "rust/2.0.0-beta.1",
            "csharp/2.0.0-beta.1",
            "rust/2.0.0-alpha.12",
            "typescript/2.0.0-alpha.11",
            "rust/2.0.0-alpha.11",
            "python/2.0.0a11",
            "csharp/2.0.0-alpha.11",
            "csharp/2.0.0-alpha.10",
            "rust/2.0.0-alpha.10",
            "typescript/2.0.0-alpha.10",
            "python/2.0.0a10",
            "rust/2.0.0-alpha.9",
            "typescript/2.0.0-alpha.9",
            "python/2.0.0a9",
            "csharp/2.0.0-alpha.9",
            "rust/2.0.0-alpha.8",
            "typescript/2.0.0-alpha.8",
            "python/2.0.0a8",
            "csharp/2.0.0-alpha.8",
            "typescript/2.0.0-alpha.7",
            "csharp/2.0.0-alpha.7",
            "python/2.0.0a7",
            "csharp/2.0.0-alpha.6",
            "typescript/2.0.0-alpha.6",
            "python/2.0.0a6",
            "csharp/2.0.0-alpha.2",
            "csharp/2.0.0-alpha.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53597.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:44.322152634Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53597.json",
        "https://github.com/microsoft/prompty/security/advisories/GHSA-c4gh-rv8h-q9vw",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-53597",
        "https://github.com/microsoft/prompty/commit/c27402da2487075be577f06aa79df627fb9d6853"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-94"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53597.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-53597",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 512423,
  "published_at": "2026-07-16T14:54:55.075+00:00"
}