Mozilla Firefox and Thunderbird Sandbox Escape and Remote Code Execution Vulnerability via IPC Parameter Validation Flaw (CVE-2019-11708)

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2019-11708) is an input validation flaw (CWE-20) within the Inter-Process Communication (IPC) mechanism of Mozilla Firefox and Thunderbird's multi-process architecture. The root cause lies in the insufficient vetting of parameters passed with the 'Prompt:Open' IPC message from a low-privilege child process (renderer) to the high-privilege parent process. Because the parent process fails to properly sanitize these parameters, it can be coerced into opening arbitrary web content outside the sandbox environment.

2. Exploitation Mechanics & Attack Scenario

In a standard multi-process browser architecture, the renderer process is heavily sandboxed to prevent system-level compromise. However, in this attack scenario, an attacker first compromises the child process (typically via a separate memory corruption vulnerability). Once control is established, the attacker crafts and sends a malicious 'Prompt:Open' IPC message to the parent process. The parent process processes this message without validation, executing the attacker-specified web content in the context of the non-sandboxed parent. When chained with other vulnerabilities, this allows full sandbox escape and arbitrary code execution on the host operating system.

3. Infrastructure & Business Impact

With a CVSS score of 10.0 and active exploitation history (listed in CISA KEV), this vulnerability poses an extreme risk to enterprise endpoints. Successful exploitation allows remote attackers to gain full control of the victim's machine upon visiting a malicious website. This can serve as an initial access vector for corporate network intrusion, leading to data exfiltration, ransomware deployment, and lateral movement across internal infrastructure.