CVE-2021-40373
📋 TL;DR
CVE-2021-40373 is a critical remote code execution vulnerability in playSMS that allows attackers to execute arbitrary PHP code on affected systems. This affects playSMS installations before version 1.4.5 where attackers can inject PHP code through the configuration interface and trigger execution via a specific URL. Organizations using vulnerable playSMS versions for SMS gateway functionality are at risk.
💻 Affected Systems
- playSMS
📦 What is this software?
Playsms by Playsms
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, steal data, install malware, pivot to other systems, and maintain persistent access.
Likely Case
Attackers gain web server user privileges, allowing them to read/write files, access databases, and potentially escalate to full system control.
If Mitigated
Limited impact if proper network segmentation, web application firewalls, and least privilege principles are implemented.
🎯 Exploit Status
Exploit requires administrative credentials to inject code initially, but once injected, execution can be triggered without authentication via the vulnerable URI.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.4.5 and later
Vendor Advisory: https://playsms.org/2021/09/04/playsms-1-4-5-released/
Restart Required: No
Instructions:
1. Backup your current playSMS installation and database. 2. Download playSMS 1.4.5 or later from the official website. 3. Replace the vulnerable files with the patched version. 4. Verify the installation is working correctly.
🔧 Temporary Workarounds
Restrict access to vulnerable URI
linuxBlock access to the vulnerable index.php endpoint that triggers code execution
# For Apache: Add to .htaccess
RewriteRule ^index\.php\?app=main&inc=core_welcome - [F,L]
# For Nginx: Add to server block
location ~* /index\.php\?app=main&inc=core_welcome { deny all; }
Remove configuration write permissions
linuxMake configuration files read-only to prevent PHP code injection
chmod 444 /path/to/playsms/config/*
chown root:root /path/to/playsms/config/*
🧯 If You Can't Patch
- Implement strict network access controls to limit who can access the playSMS web interface
- Deploy a web application firewall (WAF) with rules to block PHP code injection and execution attempts
🔍 How to Verify
Check if Vulnerable:
Check if playSMS version is below 1.4.5 by examining the version file or checking the web interface footerCheck Version:
grep -r "_version" /path/to/playsms/ | grep -i versionVerify Fix Applied:
Verify version is 1.4.5 or higher and test that PHP code cannot be executed via the vulnerable URI📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to configuration pages
- Requests to index.php?app=main&inc=core_welcome with suspicious parameters
- PHP execution errors in web server logs
Network Indicators:
- Unusual outbound connections from the playSMS server
- Traffic patterns indicating command and control communication
SIEM Query:
source="web_server_logs" AND (uri="*index.php?app=main&inc=core_welcome*" OR message="*PHP code execution*" OR message="*eval()*" OR message="*system()*")