{"cve":"CVE-2026-35209","nvd":{"published":"2026-04-06T18:16:44.157","modified":"2026-07-21T19:10:00.107","status":"Analyzed","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5},"cwes":["CWE-1321"],"references":["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"],"products":["unjs:defu"],"source":"nvd","synced_at":"2026-10-19T22:28:59.047572785+00:00"},"epss":{"cve":"CVE-2026-35209","score":0.00398,"percentile":0.34085,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-737v-mqg7-c878","url":"https://osv.dev/vulnerability/GHSA-737v-mqg7-c878","summary":"defu: Prototype pollution via `__proto__` key in defaults argument","modified":"2026-09-10T03:50:43.584391111Z","packages":[{"ecosystem":"npm","name":"defu","purl":"pkg:npm/defu","ranges":["<6.1.5"],"fixed":["6.1.5"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}