libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes

{
  "id": "ed3e46353e7bda0d044975125c4d042069fd50a2a34533311455a6f92670b499",
  "url": "https://www.cve.org/CVERecord?id=CVE-2026-118370",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes",
    "summary": "libexpat through 2.9.0 contains a signed integer overflow vulnerability in storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds writes via oversized attribute counts. Attackers can supply a multi-gigabyte document with a start tag carrying over 2^30 attributes to overflow attIndex and nPrefixes, crashing applications or corrupting heap memory.",
    "evidence": "cve:CVE-2026-118370",
    "products": [
      {
        "name": {
          "value": "libexpat",
          "evidence": "/containers/cna/affected/0/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-118370",
      "aliases": [
        "CVE-2026-118370"
      ],
      "metrics": [
        {
          "format": "CVSS",
          "cvssV4_0": {
            "version": "4.0",
            "baseScore": 8.2,
            "attackVector": "NETWORK",
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
            "userInteraction": "NONE",
            "attackComplexity": "HIGH",
            "attackRequirements": "PRESENT",
            "privilegesRequired": "NONE",
            "subIntegrityImpact": "NONE",
            "vulnIntegrityImpact": "NONE",
            "subAvailabilityImpact": "NONE",
            "vulnAvailabilityImpact": "HIGH",
            "subConfidentialityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE"
          }
        },
        {
          "format": "CVSS",
          "cvssV3_1": {
            "scope": "UNCHANGED",
            "version": "3.1",
            "baseScore": 5.9,
            "attackVector": "NETWORK",
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "integrityImpact": "NONE",
            "userInteraction": "NONE",
            "attackComplexity": "HIGH",
            "availabilityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "confidentialityImpact": "NONE"
          }
        }
      ],
      "affected": [
        {
          "repo": "https://github.com/libexpat/libexpat",
          "vendor": "libexpat",
          "product": "libexpat",
          "versions": [
            {
              "status": "affected",
              "version": "0",
              "versionType": "semver",
              "lessThanOrEqual": "2.9.0"
            }
          ],
          "packageURL": "pkg:github/libexpat/libexpat",
          "defaultStatus": "unaffected"
        }
      ],
      "modified": "2026-10-28T02:03:19.447Z",
      "provider": "cve",
      "references": [
        "https://github.com/libexpat/libexpat/pull/1450",
        "https://github.com/libexpat/libexpat/commit/1bac53c4fc460a03cd9860f39501c7979f6750ae",
        "https://github.com/libexpat/libexpat/commit/621cb2c78b253ee023a86bc91d6ddb048481c04c",
        "https://github.com/libexpat/libexpat/blob/a76b1174c1ea52abb639a4c69d52b630a8a106a2/expat/lib/xmlparse.c#L4138-L4140",
        "https://github.com/libexpat/libexpat",
        "https://www.vulncheck.com/advisories/libexpat-through-2.9.0-integer-overflow-in-storeatts-via-attindex-and-nprefixes"
      ],
      "provider_metadata": {
        "cna": {
          "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
          "shortName": "VulnCheck",
          "dateUpdated": "2026-10-28T02:03:19.447Z"
        }
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-118370",
        "evidence": "/cveMetadata/cveId"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/containers/cna/metrics"
  },
  "source_id": "core-cve",
  "document_id": 406281,
  "published_at": "2026-10-28T02:03:19.447+00:00"
}