libexpat through 2.9.0 Denial of Service via Billion Laughs Detection Delay

{
  "id": "c0f9d6bc46a8c80c875ced64ae8e8aa3f0257ebb494aab8e712b57108ae276c7",
  "url": "https://osv.dev/vulnerability/CVE-2026-115506",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "libexpat through 2.9.0 Denial of Service via Billion Laughs Detection Delay",
    "summary": "libexpat through 2.9.0 contains a denial of service vulnerability because billion laughs protection in accountingDiffTolerated() in xmlparse.c detects entity amplification too late. Attackers can supply a moderately sized XML document with a large DTD and nested entity expansions to consume tens of seconds of CPU per parse.",
    "evidence": "osv:CVE-2026-115506",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-115506",
      "aliases": [
        "CVE-2026-115506"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/libexpat/libexpat",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "last_affected": "a76b1174c1ea52abb639a4c69d52b630a8a106a2"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "2.9.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "2.9.0"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "versions": [
            "R_2_9_0",
            "R_2_8_5",
            "R_2_8_4",
            "R_2_8_3",
            "R_2_8_2",
            "R_2_8_1",
            "R_2_8_0",
            "R_2_7_5",
            "R_2_7_4",
            "R_2_7_3",
            "R_2_7_2",
            "R_2_7_1",
            "R_2_7_0",
            "R_2_6_4",
            "R_2_6_3",
            "R_2_6_2",
            "R_2_6_1",
            "R_2_6_0",
            "R_2_5_0",
            "R_2_4_9",
            "R_2_4_8",
            "R_2_4_7",
            "R_2_4_6",
            "R_2_4_5",
            "R_2_4_4",
            "R_2_4_3",
            "R_2_4_2",
            "R_2_4_1",
            "R_2_4_0",
            "R_2_3_0",
            "R_2_2_10",
            "R_2_2_9",
            "R_2_2_8",
            "R_2_2_7",
            "R_2_2_6",
            "R_2_2_5",
            "R_2_2_4",
            "R_2_2_3",
            "R_2_2_2",
            "R_2_2_1",
            "R_2_2_0",
            "R_2_1_1",
            "R_2_1_0",
            "R_2_0_1",
            "R_2_0_0",
            "R_1_95_8",
            "R_1_95_7",
            "R_1_95_6",
            "R_1_95_5",
            "R_1_95_4",
            "R_1_95_3",
            "R_1_95_2",
            "R_1_95_0",
            "libexpat-alpha-1",
            "start",
            "sourceforge_init",
            "jclark-orig",
            "V20000512",
            "V19991013",
            "V19990728",
            "V19990709",
            "V19990626",
            "V1_1",
            "V19990425",
            "V1990307",
            "V19990109",
            "V19981231",
            "V19981122",
            "V1_0",
            "beta4",
            "beta3",
            "beta2",
            "REC1_0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-115506.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:48.601626496Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/115xxx/CVE-2026-115506.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-115506",
        "https://www.vulncheck.com/advisories/libexpat-through-2.9.0-denial-of-service-via-billion-laughs-detection-delay",
        "https://github.com/libexpat/libexpat/issues/1160",
        "https://github.com/libexpat/libexpat/pull/1433",
        "https://github.com/libexpat/libexpat",
        "https://github.com/hannob/lololol"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-776"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/115xxx/CVE-2026-115506.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-115506",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 517083,
  "published_at": "2026-10-22T19:14:06.001+00:00"
}