{"id":"CVE-2026-55091","title":"flat-to-nested converts a hierarchy from a flat representation to a nested representation","summary":"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…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","cwe":["CWE-915","CWE-1321"],"vendor":"joaonuno","product":"flat-to-nested-js","affected":["flat-to-nested-js < 1.1.2"],"patched":["flat-to-nested 1.1.2"],"published":"2026-09-14","updated":"2026-09-14","sourceUpdated":"2026-09-14T20:16:47.163","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-55091","references":[{"url":"https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f","label":"security-advisories@github.com"},{"url":"https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2","label":"security-advisories@github.com"},{"url":"https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4","label":"security-advisories@github.com"},{"url":"https://github.com/advisories/GHSA-hp36-v28f-w3r4"}],"tags":["nvd","cve.org","ghsa","npm"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-09-14T19:22:11.687253Z"},"ecosystem":"npm","ingestedAt":"2026-06-22T13:35:24.388Z","epss":0.00355,"epssPercentile":0.29224,"slug":"CVE-2026-55091","body":"## Overview\n\nflat-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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Package advisory (CVE-2026-55091)\n\nAffected packages:\n\n- `flat-to-nested <= 1.1.1`\n\nPatched in:\n\n- `flat-to-nested 1.1.2`\n\nSource: https://github.com/advisories/GHSA-hp36-v28f-w3r4","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}