0-Day Exploit Hits FreePBX Servers, Admins Warned to Cut Internet Access

FreePBX administrators are racing to secure their systems following the disclosure of a critical zero-day vulnerability in the commercial Endpoint Manager (Endpoint) module.

First observed on August 21, compromised systems began exhibiting erratic behavior and unauthorized configuration changes, prompting an emergency advisory from Sangoma’s FreePBX Security Team on August 26.

The flaw, classified as an unauthenticated privilege escalation leading to remote code execution (RCE), allows attackers to gain administrative privileges without valid credentials when the Admin UI is exposed to hostile networks.

class="wp-block-heading" id="immediate-mitigation-and-emergency-response">Immediate Mitigation and Emergency Response

Upon detection, operators must immediately isolate affected systems to prevent further exploitation. The quickest mitigation is to block public access to ports 80 and 443—used by the Admin UI—via firewall rules.

For example, using iptables:

bashiptables -I INPUT -p tcp --dport 443 -s 198.51.100.25 -j ACCEPT   # allow trusted admin IP
iptables -I INPUT -p tcp --dport 443 -j DROP                    # block all other HTTPS
iptables -I INPUT -p tcp --dport 80 -j DROP                     # block HTTP

Network segmentation is also recommended: place the PBX behind a VPN or on a dedicated management VLAN.

Administrators should verify the presence of the Endpoint module by checking the /var/www/html/admin/modules/endpoint directory and ensuring they have applied the vendor’s hotfix or updated to the patched EDGE module version as per the advisory.

Detection efforts must include scanning web server logs for unusual POST requests targeting /admin/modules/endpoint and reviewing recently modified files under the PBX webroot.

Operators can leverage the community-supplied forensic collection script, collect_forensics_freepbx.sh, which automates artifact gathering:

bash./collect_forensics_freepbx.sh --dest /secure/forensics --confirm

This script preserves file ownership and timestamps, centralizing logs, configuration files, and core dumps for offline analysis.

Remediation, Forensics, and Long-Term Hardening

Once immediate containment is achieved, administrators should apply the official patch issued on August 26 or remove the vulnerable module entirely until a secure version is confirmed.

Change all administrative credentials, rotate API keys, and inspect dialplan configurations and custom scripts for unauthorized backdoors or injected perl/php payloads.

Full forensic analysis should include:

• Web server and PHP-FPM logs for anomalous entries
• AIDE or Tripwire snapshots to detect file-system tampering
• Memory dumps for suspicious processes listening on ephemeral ports

Community-driven data has revealed that compromised hosts often exhibit indicators of compromise such as new cronjobs invoking curl to remote payloads and base64-encoded commands executed via eval().

Administrators should search for patterns like base64_decode in *.php files and validate the integrity of core Endpoint Manager scripts.

In the long term, best practices include disabling unused commercial modules, enforcing MFA for admin access, and conducting regular automated vulnerability scans with tools like OpenVAS or Nessus.

By combining emergency isolation, thorough forensic analysis, and proactive hardening, organizations can mitigate the impact of the Aug 2025 zero-day and bolster their FreePBX defenses.

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