{"id":"CVE-2026-33228","summary":"flatted: Prototype Pollution via parse()","details":"flatted is a circular JSON parser. Prior to version 3.4.2, the parse() function in flatted can use attacker-controlled string values from the parsed JSON as direct array index keys, without validating that they are numeric. Since the internal input buffer is a JavaScript Array, accessing it with the key \"__proto__\" returns Array.prototype via the inherited getter. This object is then treated as a legitimate parsed value and assigned as a property of the output object, effectively leaking a live reference to Array.prototype to the consumer. Any code that subsequently writes to that property will pollute the global prototype. This issue has been patched in version 3.4.2.","aliases":["GHSA-rf6f-7fwh-wjgh"],"modified":"2026-09-08T03:30:51.868420401Z","published":"2026-03-20T23:06:48.485Z","database_specific":{"cna_assigner":"GitHub_M","cwe_ids":["CWE-1321"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33228.json"},"references":[{"type":"WEB","url":"https://github.com/WebReflection/flatted/releases/tag/v3.4.2"},{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33228.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:13826"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:34342"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:9742"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-33228"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33228.json"},{"type":"ADVISORY","url":"https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33228"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2449872"},{"type":"FIX","url":"https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/webreflection/flatted","events":[{"introduced":"0"},{"fixed":"3bf09091c3562e17a0647bc06710dd6097079cf7"},{"fixed":"885ddcc33cf9657caf38c57c7be45ae1c5272802"}],"database_specific":{"source":["CPE_RANGE","REFERENCES"],"cpe":"cpe:2.3:a:webreflection:flatted:*:*:*:*:*:node.js:*:*","extracted_events":[{"introduced":"0"},{"fixed":"3.4.2"}]}}],"versions":["v3.4.1","v3.4.0","v3.3.4","v3.3.3","v3.3.2","v3.3.1","v3.3.0","v3.2.13","v3.2.12","v3.2.11","v3.2.10","v3.2.8","v3.2.7","v3.2.6","v3.2.5","v3.2.4","v3.2.3","v3.2.2","v3.2.1","v3.2.0","v3.1.1","v3.0.5","v3.0.4","v3.0.3","v3.0.2","v3.0.1","v3.0.0","v2.0.2","v2.0.1","v2.0.0","v1.0.3","v1.0.2","v1.0.1","v1.0.0","v0.2.3","v0.2.2","v0.2.1","v0.2.0","v0.1.0"],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-33228.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P"}]}