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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Attack Requirements
None
No additional conditions
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
High
Complete denial of service
CVSS Vector v4.0
Weakness Type (CWE)
Vulnerable Products 1
| Configuration | From (including) | Up to (excluding) |
|---|---|---|
|
Webreflection Flatted
cpe:2.3:a:webreflection:flatted:*:*:*:*:*:node.js:*:*
|
— |
3.4.2
|
References 3
https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae…
security-advisories@github.com
https://github.com/WebReflection/flatted/releases/tag/v3.4.2
security-advisories@github.com
https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh
security-advisories@github.com