{"id":"CVE-2026-33228","aliases":["GHSA-rf6f-7fwh-wjgh"],"url":"https://o3.security/vulnerability/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.","published":"2026-03-20T23:06:48.485Z","modified":"2026-08-06T03:31:07.528222839Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"flatted","fixedVersion":"3.4.2"}],"fix":{"url":"https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802","label":"WebReflection/flatted@885ddcc"},"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-06T03:31:07.528222839Z"}}