Google Chrome V8 Engine Array.prototype.concat Out-of-Bounds Read and Remote Code Execution Vulnerability (CVE-2016-1646)

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2016-1646) resides in the Array.prototype.concat implementation within builtins.cc of the Google V8 JavaScript engine, as integrated into Google Chrome. The V8 engine optimizes array operations by tracking and handling specific ElementsKind types. However, a logical flaw in the concatenation logic fails to properly validate and handle dynamic changes in element data types during execution. This oversight leads to an Out-of-Bounds (OOB) Read (CWE-125), where the engine accesses memory outside the allocated boundaries of the target array.

2. Exploitation Mechanics & Attack Scenario

An attacker can exploit this vulnerability by serving a malicious JavaScript payload designed to manipulate array structures. By defining custom getters or modifying the array's prototype chain, the attacker can dynamically alter the array's length or element type mid-operation. When Array.prototype.concat is invoked, V8 relies on outdated or mismatched type assumptions, copying memory based on incorrect size parameters. This mismatch allows the attacker to read adjacent heap memory, leak sensitive pointers, bypass security mitigations like ASLR, and ultimately achieve arbitrary code execution within the browser's renderer process.

3. Infrastructure & Business Impact

As a vulnerability listed in the CISA KEV catalog, CVE-2016-1646 represents a highly reliable vector for real-world exploitation. Successful exploitation allows remote attackers to compromise user endpoints silently when users visit a compromised or malicious website. This can lead to initial access into corporate networks, credential theft, and subsequent lateral movement, posing severe risks to organizational data integrity and business continuity.