{"id":"CVE-2026-55091","summary":"flat-to-nested: Prototype pollution in flat-to-nested convert() via __proto__ parent/id key","details":"flat-to-nested converts a hierarchy from a flat representation to a nested representation. Prior to 1.1.2, FlatToNested.prototype.convert in index.js uses attacker-influenced id and parent record fields directly as keys in the plain temp and pendingChildOf objects. When parent or id is __proto__, temp[parent] can resolve to Object.prototype, and initPush() can write attacker-controlled data to the global children prototype property while existing prototype methods remain intact. Any application that passes attacker-influenced flat records to convert() can therefore expose unrelated objects to polluted inherited state, causing application-logic corruption or denial of service and potentially enabling greater impact when a downstream prototype-pollution gadget is present. The constructor and prototype strings are also unsafe inherited-key values in the same lookup design. This issue is fixed in version 1.1.2.","aliases":["GHSA-hp36-v28f-w3r4"],"modified":"2026-09-16T03:47:00.805062329Z","published":"2026-09-14T17:26:38.877Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55091.json","cna_assigner":"GitHub_M","cwe_ids":["CWE-1321","CWE-915"]},"references":[{"type":"WEB","url":"https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55091.json"},{"type":"ADVISORY","url":"https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55091"},{"type":"FIX","url":"https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/joaonuno/flat-to-nested-js","events":[{"introduced":"0"},{"fixed":"680a5ebe1194edda16fa93baaa56ff14fe0e3d7f"},{"fixed":"bea35426afae09a9150ff0100045b64d40101a30"}],"database_specific":{"source":["AFFECTED_FIELD","REFERENCES"],"extracted_events":[{"introduced":"0"},{"fixed":"1.1.2"}]}}],"versions":["v1.1.1","v1.1.0","v1.0.2","v1.0.1","v1.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55091.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"}]}