{"id":"CVE-2026-33228","title":"flatted is a circular JSON parser","summary":"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 int…","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-1321","CWE-915"],"published":"2026-03-20","updated":"2026-06-27","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-33228","references":[{"url":"https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802","label":"security-advisories@github.com"},{"url":"https://github.com/WebReflection/flatted/releases/tag/v3.4.2","label":"security-advisories@github.com"},{"url":"https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh","label":"security-advisories@github.com"},{"url":"https://access.redhat.com/errata/RHSA-2026:13826","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/errata/RHSA-2026:9742","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://access.redhat.com/security/cve/CVE-2026-33228","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2449872","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33228.json","label":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c"}],"tags":["nvd"],"epss":0.00808,"epssPercentile":0.55338,"ingestedAt":"2026-06-29T13:24:34.809Z","slug":"CVE-2026-33228","body":"## Overview\n\nflatted 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.2,"exploitation":0,"ransomware":0},"changes":[]}