CVE-2016-8496 in FortiOS
Summary
by MITRE
A potential execution of unauthorized code or commands vulnerability in Fortinet FortiClient SSL_VPN Linux versions available with FortiOS 5.4.2 and below allows attacker to potentially overwrite an existing file via the FortiClient log file.
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Analysis
by VulDB Data Team • 12/25/2020
The vulnerability identified as CVE-2016-8496 represents a significant security flaw in Fortinet FortiClient SSL_VPN Linux implementations running on FortiOS versions 5.4.2 and earlier. This issue stems from inadequate input validation and file handling mechanisms within the SSL_VPN client software, creating an avenue for malicious actors to execute unauthorized code or commands through strategic manipulation of log file operations. The vulnerability specifically targets the way the FortiClient processes log file data, allowing attackers to potentially overwrite existing files on the target system through carefully crafted log entries.
The technical exploitation of this vulnerability occurs through a path traversal or file overwrite attack vector where an attacker can manipulate the logging functionality to write arbitrary data to files that should normally be protected or restricted. This flaw falls under the CWE-22 category of Path Traversal and CWE-73 hardcoded file name references, as the application fails to properly validate or sanitize file paths used in log operations. The vulnerability essentially allows an attacker to bypass normal file access controls and potentially execute code or commands by leveraging the logging subsystem to modify critical system files or replace existing legitimate files with malicious content.
The operational impact of CVE-2016-8496 extends beyond simple file overwrites, as it creates a persistent threat vector that could lead to complete system compromise. An attacker who successfully exploits this vulnerability could potentially overwrite system binaries, configuration files, or other critical components, enabling them to establish persistent access or escalate privileges within the compromised environment. The attack surface is particularly concerning for Linux environments where FortiClient SSL_VPN is deployed, as it provides an entry point that could be leveraged in conjunction with other attack techniques to achieve broader system compromise. This vulnerability also aligns with ATT&CK technique T1059 for command and scripting interpreter and T1070 for indicator removal, as successful exploitation could enable attackers to execute commands and potentially hide their activities through log manipulation.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected FortiOS versions, with administrators upgrading to FortiOS 5.4.3 or later where the issue has been addressed. Organizations should implement strict access controls and monitoring of log file operations, particularly in environments where FortiClient SSL_VPN is deployed. Network segmentation and least privilege principles should be enforced to limit the potential impact of successful exploitation. Security monitoring solutions should be configured to detect anomalous file modification patterns and unusual log file activities that could indicate exploitation attempts. Additionally, regular security assessments and penetration testing should be conducted to identify and remediate similar vulnerabilities in the broader network infrastructure, as this type of flaw often indicates broader security weaknesses in the application's input validation and file handling mechanisms.