CVE-2026-33228

Description

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.

Risk Information

Base Score

9.8

MODERATE

Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score

Exploitation Probability

0.049

Associated Vulnerability

Vulnerability	OS Platform
Multiple Vulnerabilities are affected in IBM App Connect Enterprise 13.0.6.2	Windows
Multiple Vulnerabilities are affected in IBM App Connect Enterprise 12.0.12.24	Windows

Patch Details

No records found

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234