CVE-2019-9971
📋 TL;DR
This vulnerability allows local attackers to gain root privileges on 3CX Phone System installations by exploiting insecure sudo permissions for tcpdump. The -z option in tcpdump can execute arbitrary commands when combined with sudo without password requirements. Affects 3CX Phone System users with Debian-based installations.
💻 Affected Systems
- 3CX Phone System
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with root access, allowing installation of persistent backdoors, data exfiltration, and lateral movement within the network.
Likely Case
Local privilege escalation to root by authenticated users or attackers who gain initial access, leading to full control of the phone system.
If Mitigated
Limited impact with proper sudo restrictions and network segmentation, though local users could still exploit if they gain access.
🎯 Exploit Status
Exploit requires local access. The sudo configuration allows tcpdump with -z option to execute arbitrary commands as root.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to latest 3CX version (beyond 16.0.0.1570)
Vendor Advisory: https://www.3cx.com/blog/releases/v16-update-5-security/
Restart Required: Yes
Instructions:
1. Backup configuration and recordings. 2. Update 3CX Phone System to latest version via management console. 3. Restart services. 4. Verify sudo permissions are restricted.
🔧 Temporary Workarounds
Restrict sudo tcpdump permissions
linuxRemove or restrict sudo permissions for tcpdump to prevent command execution via -z option.
sudo visudo
Remove or modify line: <username> ALL=(ALL) NOPASSWD: /usr/sbin/tcpdump
Remove tcpdump -z option capability
linuxConfigure sudo to disallow the -z option when running tcpdump.
sudo visudo
Change to: <username> ALL=(ALL) NOPASSWD: /usr/sbin/tcpdump !-z*
🧯 If You Can't Patch
- Implement strict sudoers configuration to remove tcpdump privileges or require password authentication.
- Restrict local access to the system and implement network segmentation to limit attack surface.
🔍 How to Verify
Check if Vulnerable:
Check sudoers file: sudo cat /etc/sudoers | grep tcpdump. If tcpdump appears with NOPASSWD and no -z restriction, system is vulnerable.Check Version:
sudo dpkg -l | grep 3cx-phone-systemVerify Fix Applied:
Verify sudoers configuration no longer allows tcpdump with NOPASSWD, or check 3CX version is updated beyond 16.0.0.1570.📡 Detection & Monitoring
Log Indicators:
- sudo logs showing tcpdump execution with -z option
- Unauthorized root access attempts in auth.log
Network Indicators:
- Unusual outbound connections from phone system server
- Unexpected tcpdump processes running
SIEM Query:
source="auth.log" AND "sudo.*tcpdump.*-z" OR source="syslog" AND "COMMAND=/usr/sbin/tcpdump"🔗 References
- https://www.gosecure.net/blog
- https://www.gosecure.net/blog/2022/05/31/security-advisory-multiple-vulnerabilities-impact-3cx-phone-system/
- https://www.securusglobal.com/community/2014/03/17/how-i-got-root-with-sudo/
- https://www.gosecure.net/blog
- https://www.gosecure.net/blog/2022/05/31/security-advisory-multiple-vulnerabilities-impact-3cx-phone-system/
- https://www.securusglobal.com/community/2014/03/17/how-i-got-root-with-sudo/
