CVE-2026-35209

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{"affected": [{"affectedData": [{"product": "defu", "vendor": "unjs", "versions": [{"status": "affected", "version": "< 6.1.5"}]}], "source": "security-advisories@github.com"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:unjs:defu:*:*:*:*:*:node.js:*:*", "matchCriteriaId": "8AEDDCDC-B8A2-4F55-8E3C-6CDC5843122B", "versionEndExcluding": "6.1.5", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "defu is software that allows uers to assign default properties recursively. Prior to version 6.1.5, applications that pass unsanitized user input (e.g. parsed JSON request bodies, database records, or config files from untrusted sources) as the first argument to `defu()` are vulnerable to prototype pollution. A crafted payload containing a `__proto__` key can override intended default values in the merged resul. The internal `_defu` function used `Object.assign({}, defaults)` to copy the defaults object. `Object.assign` invokes the `__proto__` setter, which replaces the resulting object's `[[Prototype]]` with attacker-controlled values. Properties inherited from the polluted prototype then bypass the existing `__proto__` key guard in the `for...in` loop and land in the final result. Version 6.1.5 replaces `Object.assign({}, defaults)` with object spread (`{ ...defaults }`), which uses `[[DefineOwnProperty]]` and does not invoke the `__proto__` setter."}, {"lang": "es", "value": "defu es un software que permite a los usuarios asignar propiedades predeterminadas recursivamente. Antes de la versi\u00f3n 6.1.5, las aplicaciones que pasan entrada de usuario no saneada (p. ej., cuerpos de solicitud JSON analizados, registros de base de datos o archivos de configuraci\u00f3n de fuentes no confiables) como el primer argumento a 'defu()' son vulnerables a la contaminaci\u00f3n de prototipos. Una carga \u00fatil manipulada que contiene una clave '__proto__' puede anular los valores predeterminados previstos en el resultado fusionado. La funci\u00f3n interna '_defu' usaba 'Object.assign({}, defaults)' para copiar el objeto de valores predeterminados. 'Object.assign' invoca al setter '__proto__', que reemplaza el '[[Prototype]]' del objeto resultante con valores controlados por el atacante. Las propiedades heredadas del prototipo contaminado luego eluden la protecci\u00f3n de clave '__proto__' existente en el bucle 'for...in' y terminan en el resultado final. La versi\u00f3n 6.1.5 reemplaza 'Object.assign({}, defaults)' con la propagaci\u00f3n de objetos ('{ ...defaults }'), que usa '[[DefineOwnProperty]]' y no invoca al setter '__proto__'."}], "id": "CVE-2026-35209", "lastModified": "2026-07-21T19:10:00.107", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 3.6, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-35209", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-04-06T18:49:21.516737Z", "version": "2.0.3"}}]}, "published": "2026-04-06T18:16:44.157", "references": [{"source": "security-advisories@github.com", "tags": ["Patch"], "url": "https://github.com/unjs/defu/commit/3942bfbbcaa72084bd4284846c83bd61ed7c8b29"}, {"source": "security-advisories@github.com", "tags": ["Issue Tracking", "Patch"], "url": "https://github.com/unjs/defu/pull/156"}, {"source": "security-advisories@github.com", "tags": ["Release Notes"], "url": "https://github.com/unjs/defu/releases/tag/v6.1.5"}, {"source": "security-advisories@github.com", "tags": ["Mitigation", "Vendor Advisory"], "url": "https://github.com/unjs/defu/security/advisories/GHSA-737v-mqg7-c878"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-1321"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,6.1.5)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "cna", "scores": [{"score": 100.0, "source": "cna"}]}, "original": {"product": "defu", "source": "cna", "vendor": "unjs"}, "product": "defu", "vendor": "unjs"}], "analysis": {"en": {"generated_at": "2026-04-06T21:37:43.489223+00:00", "value": {"mitigation_remediation": ["Update defu to version 6.1.5 or newer.", "Verify that all inputs to defu() are sanitized or derived from trusted sources.", "Review application code for other prototype pollution risks."], "summary": {"action": "Patch Now", "impact": "Prototype pollution enabling unintended property injection"}, "threat_synthesis": {"affected_systems": "The affected product is the JavaScript library defu, maintained by unjs. All releases prior to 6.1.5 are vulnerable. Applications that use defu to merge user supplied data, such as parsed JSON bodies or configuration files from untrusted sources, are at risk unless they have removed the ability to pass raw user data to defu.", "description_and_impact": "defu allows developers to merge default values into objects recursively. Before version 6.1.5, an attacker could send a payload containing a __proto__ key as part of the defaults argument. The library copied defaults with Object.assign, which triggered the __proto__ setter and replaced the prototype of the result object. This prototype pollution can allow attackers to inject arbitrary properties into the Object.prototype, potentially affecting all objects created thereafter and leading to logic bypasses or other unintended behavior.", "risk_and_exploitability": "The CVSS base score is 7.5, indicating a high potential for severe impact if exploited. The CVE is not listed in KEV and no EPSS score is available. Attacks would require sending crafted input to a defu invocation, which is likely possible via an HTTP endpoint or configuration import. Once the prototype is polluted, any subsequent object created in the same process can inherit the injected properties, allowing attackers to alter runtime behavior or bypass security checks."}}}}, "created": "2026-04-06T21:47:09.145987+00:00", "updated": "2026-04-07T09:39:13.868324+00:00", "vendors": ["unjs", "unjs$PRODUCT$defu"]}