CVE-2023-2551: Bumsys PHP Remote File Inclusion Vulnerability

CVE-2023-2551 Overview

CVE-2023-2551 is a PHP Remote File Inclusion (RFI) vulnerability discovered in the GitHub repository unilogies/bumsys prior to version 2.1.1. This vulnerability allows authenticated attackers with network access to include arbitrary remote files, potentially leading to complete system compromise through remote code execution, data exfiltration, or unauthorized access to sensitive information.

Critical Impact

Authenticated attackers can exploit this RFI vulnerability to execute arbitrary code on the target server, potentially gaining full control over the affected system and accessing sensitive data stored within the bumsys application.

Affected Products

• bumsys_project bumsys versions prior to 2.1.1
• cpe:2.3:a:bumsys_project:bumsys:*:*:*:*:*:*:*:*

Discovery Timeline

• 2023-05-05 - CVE-2023-2551 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-2551

Vulnerability Analysis

This vulnerability is classified under CWE-98 (Improper Control of Filename for Include/Require Statement in PHP Program) and CWE-829 (Inclusion of Functionality from Untrusted Control Sphere). The flaw exists in the file handling mechanism of the bumsys application where user-controlled input is passed to PHP include functions without proper validation or sanitization.

Remote File Inclusion vulnerabilities in PHP applications occur when the application dynamically includes files based on user input without properly restricting the input to local resources. In the context of bumsys, this allows an authenticated attacker to specify a URL pointing to a malicious PHP file hosted on a remote server, which is then executed in the context of the vulnerable application.

The attack requires low privileges (authenticated access) but can be executed remotely over the network without user interaction, making exploitation relatively straightforward once an attacker has valid credentials.

Root Cause

The root cause of this vulnerability lies in improper input validation for file inclusion operations within the bumsys application. The application fails to adequately restrict the file types and sources that can be included through PHP's include or require statements, allowing attackers to reference external URLs containing malicious PHP code.

The security patch addresses this by implementing stricter file type allowlisting in the .htaccess configuration, explicitly defining which file extensions are permitted.

Attack Vector

The attack vector is network-based, requiring authenticated access to the bumsys application. An attacker with valid credentials can craft a malicious request that specifies a remote URL as the file to include. When the vulnerable PHP code processes this request, it fetches and executes the remote file, allowing the attacker to run arbitrary PHP code on the server.

The following patch demonstrates the security fix applied to the .htaccess configuration:

 </IfModule>
 
 # Allow Javascript, css and images
-<FilesMatch "\.(js|css|jpg|jpeg|png|woff|woff2|ttf|ico|mp3|sql)$">
+<FilesMatch "\.(js|css|jpg|jpeg|png|woff|woff2|ttf|ico|mp3|sql|docx|doc|pdf|xls|xlsx|ppt|pptx)$">
 	<IfModule !mod_authz_core.c>
 		Allow from all
 	</IfModule>

Source: GitHub Commit Reference

Detection Methods for CVE-2023-2551

Indicators of Compromise

• Unusual outbound HTTP/HTTPS requests from the web server to unknown external domains
• Web server logs containing requests with URL parameters pointing to external file paths or URLs
• Unexpected PHP processes spawning child processes or establishing network connections
• New or modified files appearing in web-accessible directories with suspicious content

Detection Strategies

• Monitor web application logs for requests containing remote URLs in file inclusion parameters
• Implement Web Application Firewall (WAF) rules to detect and block RFI attack patterns such as http:// or https:// in unexpected parameters
• Deploy file integrity monitoring on the bumsys application directory to detect unauthorized changes
• Configure intrusion detection systems to alert on PHP processes making unexpected outbound connections

Monitoring Recommendations

• Enable verbose logging on the web server and bumsys application to capture detailed request information
• Set up alerts for authentication events followed by suspicious file access patterns
• Monitor network traffic for connections from the web server to external hosts, particularly on ports 80 and 443
• Regularly review access logs for patterns indicative of reconnaissance or exploitation attempts

How to Mitigate CVE-2023-2551

Immediate Actions Required

• Upgrade bumsys to version 2.1.1 or later immediately
• Review web server and application logs for evidence of exploitation attempts
• Audit user accounts for any unauthorized access or credential compromise
• Implement network segmentation to limit the web server's ability to make outbound connections

Patch Information

The vulnerability has been addressed in bumsys version 2.1.1. The fix is available via the official GitHub commit. Organizations should update to the latest version by pulling the most recent code from the repository and following the standard upgrade procedures for bumsys.

Additional technical details about the vulnerability discovery can be found in the Huntr Bounty Report.

Workarounds

• Disable PHP's allow_url_include directive in php.ini to prevent remote file inclusion attacks
• Implement strict input validation on all user-supplied parameters that interact with file operations
• Configure the web server to restrict outbound network access where possible
• Deploy a Web Application Firewall with rules specifically designed to block RFI attack patterns

# Disable allow_url_include in php.ini
# Edit php.ini and ensure the following setting:
allow_url_include = Off

# Verify the setting is applied
php -i | grep allow_url_include

# Restart the web server to apply changes
sudo systemctl restart apache2
# Or for nginx with PHP-FPM:
sudo systemctl restart php-fpm