CVE-2025-55211: Sangoma FreePBX RCE Vulnerability

CVE-2025-55211 Overview

CVE-2025-55211 is an authenticated command injection vulnerability in FreePBX, an open-source web-based graphical user interface for managing Asterisk PBX systems. The flaw affects versions from 17.0.19.11 up to but not including 17.0.21. Authenticated users of the Administrator Control Panel (ACP) can execute arbitrary shell commands by maliciously modifying the language settings of the framework module. The vulnerability maps to CWE-78, OS Command Injection. Sangoma resolved the issue in FreePBX release 17.0.21.

Critical Impact

Authenticated ACP users can run arbitrary operating system commands on the underlying FreePBX host, leading to full server compromise.

Affected Products

• Sangoma FreePBX 17.0.19.11 through versions prior to 17.0.21
• FreePBX framework module language configuration component
• Administrator Control Panel (ACP) interface

Discovery Timeline

• 2025-09-15 - CVE-2025-55211 published to the National Vulnerability Database (NVD)
• 2025-10-17 - Last updated in NVD database

Technical Details for CVE-2025-55211

Vulnerability Analysis

The vulnerability resides in the framework module of FreePBX, specifically in how the application processes language configuration changes initiated through the ACP. An authenticated administrator can submit crafted language values that are passed to a shell context without proper sanitization. Because the input is interpolated into a command executed by the host shell, attackers can append arbitrary commands using shell metacharacters.

Successful exploitation grants the attacker code execution under the privileges of the FreePBX web service account. On typical FreePBX deployments, this account has broad access to Asterisk configuration files, call detail records, and credentials, enabling further lateral movement and persistence.

The attack vector is network-based and requires low-privileged authentication. Exploit complexity is low, and no user interaction is required beyond the attacker's own authenticated session.

Root Cause

The framework module fails to validate and sanitize language identifier input before passing it to a shell command. This is a classic CWE-78 OS command injection pattern, where untrusted input is concatenated into a shell invocation rather than being safely passed as an argument array or whitelisted against allowed values.

Attack Vector

An attacker with valid ACP credentials, including a low-privileged administrator role, navigates to the language configuration functionality of the framework module. By submitting a malicious language value containing shell metacharacters such as ;, |, or backticks, the attacker forces the underlying shell to execute arbitrary commands. Because FreePBX is commonly exposed for remote management, credential theft or brute-force compromise of ACP accounts can escalate quickly to full host takeover.

No public proof-of-concept exploit code is available at this time. Refer to the FreePBX GitHub Security Advisory GHSA-xg83-m6q5-q24h for vendor-provided technical context.

Detection Methods for CVE-2025-55211

Indicators of Compromise

• Unexpected child processes spawned by the FreePBX web service account (typically asterisk or www-data) such as sh, bash, curl, wget, or nc.
• Modifications to language-related configuration entries in the framework module that include shell metacharacters (;, &&, |, backticks).
• Outbound network connections from the FreePBX host to unknown external IPs immediately following ACP language change events.
• New cron jobs, SSH keys, or files created in /tmp, /var/tmp, or web-writable directories shortly after administrator activity.

Detection Strategies

• Audit FreePBX web server logs for HTTP POST requests targeting framework module language endpoints with suspicious parameter values.
• Correlate ACP authentication events with subsequent process execution telemetry on the FreePBX host to identify command injection chains.
• Monitor file integrity on FreePBX configuration directories and PHP source files for unauthorized modifications.
• Hunt for anomalous shell process trees originating from the PHP-FPM or Apache worker process.

Monitoring Recommendations

• Enable verbose web access and authentication logging on the FreePBX ACP and forward logs to a centralized SIEM.
• Track all administrative configuration changes, including language and module updates, with user attribution and timestamps.
• Alert on any process execution by the FreePBX service account that is not part of the documented Asterisk runtime baseline.

How to Mitigate CVE-2025-55211

Immediate Actions Required

• Upgrade FreePBX to version 17.0.21 or later, where Sangoma has patched the language handling logic in the framework module.
• Audit all ACP administrator accounts, remove unused accounts, and rotate credentials for any account that may have been exposed.
• Restrict network access to the FreePBX ACP using firewall rules, VPN, or IP allowlisting so it is not reachable from the public internet.
• Review historical web and process logs for evidence of prior exploitation against affected versions.

Patch Information

Sangoma fixed CVE-2025-55211 in FreePBX release 17.0.21. Administrators should apply the patched release through the FreePBX module admin or the standard package update workflow. Detailed remediation guidance is available in the FreePBX GitHub Security Advisory GHSA-xg83-m6q5-q24h.

Workarounds

• If immediate patching is not possible, restrict ACP access to a small set of trusted administrators and enforce strong, unique passwords with multi-factor authentication where supported.
• Place the FreePBX management interface behind a reverse proxy or VPN that requires additional authentication before reaching the ACP.
• Temporarily disable language modification functionality for non-essential administrators by limiting role permissions in the ACP.
• Monitor the FreePBX host for unauthorized shell activity until the upgrade to 17.0.21 is completed.