High

fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)

Type: advisorySources: OSV

fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Versions 4.0.0-beta.3 through 5.5.5 contain a bypass vulnerability where numeric character references (&#NNN;, &#xHH;) and standard XML entities completely evade the entity expansion limits (e.g., maxTotalExpansions, maxExpandedLength) added to fix CVE-2026-26278, enabling XML entity expansion Denial of Service. The root cause is that replaceEntitiesValue() in OrderedObjParser.js only enforces expansion counting on DOCTYPE-defined entities while the lastEntities loop handling numeric/standard entities performs no counting at all. An attacker supplying 1M numeric entity references like A can force ~147MB of memory allocation and heavy CPU usage, potentially crashing the process—even when developers have configured strict limits. This issue has been fixed in version 5.5.6.

Products: Not specified
Affected versions: Not specified
Fixed versions: Not specified
CVEs: CVE-2026-33036
Confirmed fixed CVEs: Not specified
Updated in this feed: 7 Nov 2026, 04:50 UTC · Revision 1

Source evidence

fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)

core-osv · Original source

Published 20 Mar 2026, 05:17 UTC

osv:CVE-2026-33036

Complete source record

{
  "id": "7dd48127fd1088567da37e14fb187b48aa208c3c63dd5bd4c748c8be434e641e",
  "url": "https://osv.dev/vulnerability/CVE-2026-33036",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)",
    "summary": "fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Versions 4.0.0-beta.3 through 5.5.5 contain a bypass vulnerability where numeric character references (&#NNN;, &#xHH;) and standard XML entities completely evade the entity expansion limits (e.g., maxTotalExpansions, maxExpandedLength) added to fix CVE-2026-26278, enabling XML entity expansion Denial of Service. The root cause is that replaceEntitiesValue() in OrderedObjParser.js only enforces expansion counting on DOCTYPE-defined entities while the lastEntities loop handling numeric/standard entities performs no counting at all. An attacker supplying 1M numeric entity references like A can force ~147MB of memory allocation and heavy CPU usage, potentially crashing the process—even when developers have configured strict limits. This issue has been fixed in version 5.5.6.",
    "evidence": "osv:CVE-2026-33036",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-33036",
      "aliases": [
        "CVE-2026-33036",
        "GHSA-8gc5-j5rx-235r"
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      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
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              "type": "GIT",
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              "database_specific": {
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                        "introduced": "4.0.1"
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                  {
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                        "introduced": "4.0.0-NA"
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            "v5.0.0",
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            "v4.4.1",
            "v4.4.0",
            "v4.3.6",
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          "database_specific": {
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        }
      ],
      "modified": "2026-10-28T02:30:49.888588982Z",
      "provider": "osv",
      "references": [
        "https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.5.6",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33036.json",
        "https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-8gc5-j5rx-235r",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-33036",
        "https://github.com/NaturalIntelligence/fast-xml-parser/commit/bd26122c838e6a55e7d7ac49b4ccc01a49999a01"
      ],
      "provider_metadata": {
        "cwe_ids": [
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        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33036.json"
      }
    },
    "related_cves": [
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    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 518271,
  "published_at": "2026-03-20T05:17:03.29+00:00"
}