CVE-2023-42791: Fortinet FortiManager Path Traversal Flaw

CVE-2023-42791 Overview

CVE-2023-42791 is a relative path traversal vulnerability affecting Fortinet FortiManager, a centralized management platform for FortiGate devices. This security flaw allows authenticated attackers to execute unauthorized code or commands by sending crafted HTTP requests to vulnerable FortiManager instances. The vulnerability stems from improper validation of user-supplied input in file path operations, enabling attackers to traverse directories and potentially access or modify sensitive files outside the intended directory structure.

Critical Impact

Successful exploitation of this path traversal vulnerability can lead to unauthorized code execution, potentially compromising the integrity of the entire FortiManager deployment and any managed FortiGate devices within the network infrastructure.

Affected Products

• Fortinet FortiManager version 7.4.0
• Fortinet FortiManager versions 7.2.0 through 7.2.3
• Fortinet FortiManager versions 7.0.0 through 7.0.8
• Fortinet FortiManager versions 6.4.0 through 6.4.12
• Fortinet FortiManager versions 6.2.0 through 6.2.11

Discovery Timeline

• 2024-02-20 - CVE CVE-2023-42791 published to NVD
• 2024-12-16 - Last updated in NVD database

Technical Details for CVE-2023-42791

Vulnerability Analysis

This vulnerability is classified under CWE-23 (Relative Path Traversal) and CWE-22 (Improper Limitation of a Pathname to a Restricted Directory). The flaw exists in the HTTP request handling mechanism of FortiManager, where user-controlled input used in file path construction is not properly sanitized. Attackers with low-level privileges can leverage this weakness to escape the intended directory boundary and access files or execute commands in arbitrary locations on the filesystem.

The network-based attack vector requires no user interaction, making it particularly dangerous in environments where FortiManager is exposed to untrusted networks. Once exploited, an attacker can achieve high impact across confidentiality, integrity, and availability of the affected system, potentially gaining control over the centralized management infrastructure.

Root Cause

The root cause of CVE-2023-42791 lies in insufficient input validation and sanitization of file path parameters within FortiManager's HTTP request processing logic. When processing certain HTTP requests, the application fails to properly validate or neutralize special path elements such as ../ sequences. This allows an attacker to construct malicious paths that traverse outside the intended directory, bypassing access controls and potentially reaching sensitive system files or executables.

Attack Vector

The attack is carried out over the network by sending specially crafted HTTP requests to the FortiManager web interface. An authenticated attacker with low privileges can manipulate path parameters within these requests to include directory traversal sequences. When the application processes these malicious requests without proper validation, it resolves the path relative to the current working directory, allowing access to files and directories that should be restricted.

The vulnerability can be exploited by manipulating URL parameters or POST data containing path references. By including sequences like ../ or encoded equivalents, attackers can navigate the filesystem hierarchy and potentially read sensitive configuration files, overwrite critical system files, or execute unauthorized commands depending on the context of the vulnerable functionality.

Detection Methods for CVE-2023-42791

Indicators of Compromise

• Monitor HTTP request logs for suspicious path traversal patterns including ../, ..%2f, %2e%2e/, and similar encoded sequences in URL parameters or POST body
• Review FortiManager access logs for unusual file access patterns or requests attempting to access files outside standard application directories
• Check for unexpected modifications to system configuration files or execution of unauthorized commands on FortiManager hosts
• Analyze network traffic for crafted HTTP requests targeting FortiManager management interfaces from untrusted sources

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block path traversal sequences in HTTP requests to FortiManager
• Enable verbose logging on FortiManager and forward logs to a SIEM for correlation and anomaly detection
• Deploy network intrusion detection systems (IDS) with signatures for path traversal attacks targeting Fortinet products
• Conduct regular security assessments and vulnerability scans to identify unpatched FortiManager instances

Monitoring Recommendations

• Configure alerting for HTTP 400/403/500 error spikes that may indicate reconnaissance or exploitation attempts
• Monitor filesystem integrity on FortiManager servers using file integrity monitoring (FIM) tools
• Track authentication events and privilege usage to identify potential abuse of low-privilege accounts for exploitation
• Review audit trails for any commands executed through FortiManager that deviate from normal administrative operations

How to Mitigate CVE-2023-42791

Immediate Actions Required

• Apply the latest security patches from Fortinet to all affected FortiManager installations immediately
• Restrict network access to FortiManager management interfaces to trusted administrative networks only
• Review and audit user accounts with access to FortiManager, removing unnecessary privileges and disabling unused accounts
• Enable and monitor detailed logging on FortiManager to detect any exploitation attempts

Patch Information

Fortinet has released security updates to address this vulnerability. Administrators should upgrade FortiManager to patched versions as specified in the Fortiguard Security Advisory. The advisory (FG-IR-23-189) provides detailed information about affected versions and the recommended upgrade paths. Organizations should prioritize patching based on their exposure and the criticality of their FortiManager deployments.

Workarounds

• Implement strict network segmentation to isolate FortiManager from untrusted networks and limit access to authorized administrative hosts only
• Deploy a reverse proxy or WAF in front of FortiManager configured to filter path traversal patterns in incoming requests
• If patching cannot be performed immediately, consider temporarily disabling external access to FortiManager until updates can be applied
• Enable multi-factor authentication for all FortiManager administrative access to add an additional layer of protection

# Network ACL example to restrict FortiManager access
# Restrict management interface access to trusted admin networks
config system interface
    edit "port1"
        set allowaccess ping https ssh
        set ip 192.168.1.1 255.255.255.0
        set trusted-hosts 10.0.0.0/8 192.168.0.0/16
    next
end