{"attribution":"This product uses data from the NVD API but is not endorsed or certified by the NVD.","cve":{"id":"CVE-2026-66046","sourceIdentifier":"disclosure@vulncheck.com","published":"2026-08-18T15:16:57.000","lastModified":"2026-11-10T13:19:38.267","vulnStatus":"Modified","cveTags":[],"descriptions":[{"lang":"en","value":"Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType-\u003edefaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options."},{"lang":"es","value":"Expat hasta 2.8.3 contiene una vulnerabilidad de denegación de servicio causada por la complejidad algorítmica cuadrática en la función storeAtts() en xmlparse.c, donde el procesamiento de N atributos especificados con valores no normalizados desencadena un escaneo lineal O(N^2) de elementType  -\u003e  defaultAtts para determinar el estado CDATA. Un atacante remoto no autenticado puede suministrar un único documento XML bien formado de unos pocos megabytes a una aplicación que analiza XML no confiable para causar un consumo excesivo de CPU, lo que resulta en denegación de servicio sin requerir autenticación, resolución de entidades externas u opciones de analizador no predeterminadas."}],"affected":[{"source":"disclosure@vulncheck.com","affectedData":[{"vendor":"libexpat project","product":"libexpat","defaultStatus":"affected","repo":"https://github.com/libexpat/libexpat","packageURL":"pkg:github/libexpat/libexpat","versions":[{"version":"0","lessThanOrEqual":"2.8.3","versionType":"semver","status":"affected"}]}]},{"source":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e","affectedData":[{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)","defaultStatus":"unknown","versions":[{"version":"V3.1.7","lessThan":"*","versionType":"custom","status":"affected"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0)","defaultStatus":"unknown","versions":[{"version":"V3.1.7","lessThan":"*","versionType":"custom","status":"affected"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0)","defaultStatus":"unknown","versions":[{"version":"V3.1.7","lessThan":"*","versionType":"custom","status":"affected"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0)","defaultStatus":"unknown","versions":[{"version":"V3.1.7","lessThan":"*","versionType":"custom","status":"affected"}]},{"vendor":"Siemens","product":"SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)","defaultStatus":"unknown","versions":[{"version":"V3.1.7","lessThan":"*","versionType":"custom","status":"affected"}]}]}],"metrics":{"cvssMetricV40":[{"source":"disclosure@vulncheck.com","type":"Secondary","cvssData":{"version":"4.0","vectorString":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","baseScore":8.7,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}],"cvssMetricV31":[{"source":"disclosure@vulncheck.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":3.9,"impactScore":3.6}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-08-20T13:48:24.577412Z","id":"CVE-2026-66046","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"disclosure@vulncheck.com","type":"Secondary","description":[{"lang":"en","value":"CWE-407"}]}],"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*","versionEndIncluding":"2.8.3","matchCriteriaId":"451AFC5E-7991-4082-8CB4-C14E708CA99A"}]}]}],"references":[{"url":"https://github.com/libexpat/libexpat/pull/1321","source":"disclosure@vulncheck.com","tags":["Exploit","Patch","Vendor Advisory"]},{"url":"https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity","source":"disclosure@vulncheck.com","tags":["Exploit","Patch","Third Party Advisory"]},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-457936.html","source":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}]}}