CVE-2017-7794 in Firefox
Summary
by MITRE
On Linux systems, if the content process is compromised, the sandbox broker will allow files to be truncated even though the sandbox explicitly only has read access to the local file system and no write permissions. Note: This attack only affects the Linux operating system. Other operating systems are not affected. This vulnerability affects Firefox < 55.
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Analysis
by VulDB Data Team • 12/15/2022
This vulnerability represents a critical sandbox escape in Firefox's Linux implementation where a compromised content process can bypass file system access controls to truncate files despite the sandbox having only read permissions. The flaw exists within the sandbox broker component that manages file system operations between the restricted content process and the underlying operating system. When an attacker compromises a content process running within Firefox's sandboxed environment on Linux systems, they can exploit this weakness to manipulate file contents by truncating them, effectively creating a write operation that should not be permitted under normal sandbox constraints. The vulnerability specifically affects Firefox versions prior to 55 and demonstrates a fundamental flaw in the sandbox's permission model where read-only access is improperly extended to include destructive file operations.
The technical nature of this vulnerability stems from improper access control enforcement within the Linux sandbox implementation. The sandbox broker is designed to restrict file system operations to read-only access for content processes, yet it fails to properly validate or enforce write restrictions during truncation operations. This represents a classic case of insufficient privilege separation where the broker's file system interface does not adequately distinguish between different types of file operations, allowing truncation to proceed despite the lack of write permissions. The flaw essentially creates a path for privilege escalation where an attacker can modify file contents even though they should only be able to read them, demonstrating a failure in the sandbox's security boundary enforcement mechanisms. This issue is categorized under CWE-276, which addresses improper privilege management, and specifically relates to CWE-257, concerning the use of insecure or weak cryptographic algorithms in privilege control.
From an operational impact perspective, this vulnerability allows attackers to perform destructive file operations that could compromise system integrity and availability. Once a content process is compromised, an attacker can truncate important system files, configuration files, or user data, potentially leading to system instability, data loss, or further compromise of the affected system. The attack vector requires initial compromise of a content process, which is often achieved through other browser vulnerabilities or social engineering attacks, but once achieved, the sandbox escape provides a persistent mechanism for file manipulation. This vulnerability significantly reduces the effectiveness of Firefox's sandboxing mechanism, which is designed to limit the damage that can occur when browser components are compromised. The impact extends beyond simple file truncation to potentially enable more sophisticated attacks such as persistent backdoor creation or system-wide data corruption, particularly when combined with other exploitation techniques.
Mitigation strategies for this vulnerability involve upgrading to Firefox version 55 or later where the sandbox implementation has been corrected to properly enforce file system access controls. System administrators should implement comprehensive patch management procedures to ensure all affected Firefox installations are updated promptly. Additional protective measures include implementing network-level restrictions, monitoring for unusual file system activity, and maintaining regular backups of critical system files. The vulnerability highlights the importance of robust sandbox implementation and proper access control enforcement in browser security architectures. Organizations should also consider implementing additional security layers such as mandatory access controls, file integrity monitoring systems, and intrusion detection systems to detect and prevent exploitation attempts. This vulnerability serves as a reminder of the critical importance of proper privilege separation and access control enforcement in sandboxed environments, particularly in the context of web browser security where sandboxing is a fundamental defense mechanism. The remediation process should also include security awareness training for users to reduce the risk of initial compromise through phishing or other attack vectors that could lead to exploitation of this vulnerability.