CVE-2016-1646

What Is Chromium V8?

V8 is Google's open-source, high-performance JavaScript and WebAssembly engine, used in Chrome, Chromium, Edge, Opera, Node.js, and many other applications. V8 compiles JavaScript to native machine code using just-in-time (JIT) compilation, making JavaScript performance competitive with native code. Because V8 processes untrusted JavaScript from every web page, vulnerabilities in V8's engine — particularly in its JIT compiler, type inference, or array bounds handling — are among the highest-impact browser security issues. A memory corruption vulnerability in V8 can enable code execution in the renderer process, which can then be leveraged (with a sandbox escape) for full system compromise.

Overview

CVE-2016-1646 is an out-of-bounds read vulnerability in V8, the JavaScript engine used by Chromium-based browsers, that allows a remote attacker to execute arbitrary code or cause a denial of service via crafted JavaScript. The vulnerability can be exploited by serving malicious JavaScript to any browser using a Chromium V8 version prior to the fix — this includes Google Chrome, and potentially Chromium-based Microsoft Edge and Opera versions of the same era. Fixed in Chrome 49.0.2623.108 (March 24, 2016). CISA added CVE-2016-1646 to the KEV catalog in June 2022.

Affected Versions

Technical Details

Root Cause: Out-of-Bounds Read in V8 Array Handling

CVE-2016-1646 is an out-of-bounds read (CWE-125) in V8's JavaScript engine, specifically in how it handles JavaScript arrays or typed arrays during execution. The vulnerability occurs when V8 accesses memory beyond the declared bounds of an array object — reading data from adjacent heap memory.

While classified as an out-of-bounds read, such vulnerabilities in JIT-compiled JavaScript engines can enable code execution through:

1. Memory disclosure — the out-of-bounds read leaks adjacent heap contents, potentially revealing memory layout (defeating ASLR), object pointers, or type information
2. Type confusion — if the read value is then used as a pointer or type indicator, adjacent heap data interpreted as a V8 object can produce type confusion
3. Heap corruption — combined with a write primitive (via type confusion), the vulnerability chain can overwrite function pointers or JIT-compiled code in the renderer process
4. Renderer code execution — code executes within the Chrome renderer sandbox
5. Sandbox escape — a separate sandbox escape (often chained with a kernel LPE) is needed for full system compromise

Cross-Browser Impact

V8 is embedded in multiple browsers beyond Chrome:

• Google Chrome — primary affected browser
• Chromium — the open-source base for many browsers
• Opera (Chromium-based since 2013)
• Microsoft Edge — prior to becoming Chromium-based in 2020, Edge used Chakra rather than V8; the original Chakra-based Edge was not affected

Attack Characteristics

Discovery

Reported by anonymous researcher (or Google's Project Zero team); Google released the fix in Chrome 49.0.2623.108 on March 24, 2016.

Exploitation Context

• Browser engine exploitation: V8 vulnerabilities are among the highest-value browser exploits because they enable code execution in the renderer process for any browser using the affected V8 version; Chrome's rapid auto-update cycle limits the exposure window for patched users, but enterprise environments with managed Chrome deployments or delayed updates extend it
• Exploit kit integration: Chrome/V8 exploits are significantly more complex to weaponize reliably than Flash exploits were; CVE-2016-1646 exploitation required sophisticated heap manipulation, limiting its practical use to well-resourced actors
• Chrome sandbox: Even successful V8 exploitation only achieves code execution within Chrome's renderer sandbox — a second sandbox escape vulnerability is needed for full OS access, increasing the complexity of the full attack chain
• CISA KEV (2022): Added June 2022, reflecting confirmed exploitation

Remediation

1. Update Google Chrome — upgrade to Chrome 49.0.2623.108 or later (any current Chrome version is patched). Chrome auto-updates by default — verify automatic updates are not disabled.

2. Update other Chromium-based browsers — ensure Chromium-based browsers (Opera, older Edge) are updated to versions that include the V8 fix.

3. Enable Chrome auto-updates — ensure Chrome's auto-update mechanism is not blocked by enterprise policy or network restrictions; Chrome browser security updates should be applied rapidly.

4. Site isolation — Chrome's Site Isolation feature (enabled by default in Chrome 67+) limits the impact of renderer process compromises by separating sites into separate renderer processes.