Title: defu de unjs, Description: defu es un software que permite a los usuarios asignar propiedades predeterminadas recursivamente. Antes de la versión 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 configuración de fuentes no confiables) como el primer argumento a 'defu()' son vulnerables a la contaminación de prototipos. Una carga útil manipulada que contiene una clave '__proto__' puede anular los valores predeterminados previstos en el resultado fusionado. La función 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 protección de clave '__proto__' existente en el bucle 'for...in' y terminan en el resultado final. La versión 6.1.5 reemplaza 'Object.assign({}, defaults)' con la propagación de objetos ('{ ...defaults }'), que usa '[[DefineOwnProperty]]' y no invoca al  setter  '__proto__'.

{"timestamp":"2026-04-06T18:49:21.516737Z","id":"CVE-2026-35209","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}

[{"vendor":"unjs","product":"defu","versions":[{"version":"< 6.1.5","status":"affected"}]}]

OR
          *cpe:2.3:a:unjs:defu:*:*:*:*:*:node.js:*:* versions up to (excluding) 6.1.5

GitHub, Inc.: https://github.com/unjs/defu/commit/3942bfbbcaa72084bd4284846c83bd61ed7c8b29 Types: Patch

GitHub, Inc.: https://github.com/unjs/defu/pull/156 Types: Issue Tracking, Patch

GitHub, Inc.: https://github.com/unjs/defu/releases/tag/v6.1.5 Types: Release Notes

GitHub, Inc.: https://github.com/unjs/defu/security/advisories/GHSA-737v-mqg7-c878 Types: Mitigation, Vendor Advisory

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.

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CWE-1321

https://github.com/unjs/defu/commit/3942bfbbcaa72084bd4284846c83bd61ed7c8b29

https://github.com/unjs/defu/pull/156

https://github.com/unjs/defu/releases/tag/v6.1.5

https://github.com/unjs/defu/security/advisories/GHSA-737v-mqg7-c878