Executive Summary

CVE-2026-40520 is a command injection vulnerability in FreePBX api module version 17.0.8 and earlier. It occurs in the initiateGqlAPIProcess() function where GraphQL mutation input fields are passed directly to the PHP shell_exec() function without proper sanitization or escaping.

An authenticated user with a valid bearer token can exploit this flaw by sending a GraphQL moduleOperations mutation containing backtick-wrapped commands in the module field, which allows execution of arbitrary operating system commands on the underlying host with the privileges of the web server user.

This vulnerability arises from improper neutralization of special elements (CWE-78), enabling command injection through unsanitized shell arguments.

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Compliance Impact

CVE-2026-40520 is a command injection vulnerability that allows an authenticated user with a valid bearer token to execute arbitrary commands on the underlying host as the web server user. This can lead to unauthorized access, data manipulation, or system compromise.

Such unauthorized command execution and potential data breaches can impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of sensitive data and secure system operations.

Specifically, if exploited, this vulnerability could lead to exposure or alteration of personal or protected health information, violating confidentiality and integrity requirements mandated by these regulations.

Therefore, organizations using affected FreePBX api module versions may face compliance risks until the vulnerability is patched.

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Impact Analysis

This vulnerability allows an authenticated attacker to execute arbitrary OS commands on the server hosting the FreePBX API module with the privileges of the web server user.

Such command execution can lead to unauthorized access, data theft, system compromise, service disruption, or further escalation of privileges depending on the commands executed.

Because the attacker needs a valid bearer token, the risk is limited to authenticated users, but no additional user interaction is required to exploit the vulnerability.

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Detection Guidance

This vulnerability involves command injection via the GraphQL moduleOperations mutation in the FreePBX API module. Detection can focus on monitoring for suspicious GraphQL mutation requests that include backtick-wrapped commands in the module field, which are not normally expected.

To detect exploitation attempts on your system or network, you can monitor HTTP requests to the FreePBX API endpoint for GraphQL mutations containing suspicious shell command patterns, especially those with backticks (`).

Additionally, you can check for unexpected shell commands executed by the web server user, or unusual module operations triggered via the API.

• Use web server access logs or API logs to search for GraphQL mutation requests with the 'moduleOperations' mutation containing backtick characters.
• Example command to search logs for suspicious GraphQL mutation payloads: `grep -i 'moduleOperations' /var/log/httpd/access_log | grep '\`'`
• Monitor running processes or command history for unexpected commands executed by the web server user.
• If you have access to the FreePBX API logs or can enable verbose logging, look for GraphQL mutation inputs that include shell command injection patterns.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the FreePBX API to only trusted authenticated users, as exploitation requires a valid bearer token.

Ensure that only authorized users have API access and monitor API tokens for suspicious activity.

Apply the available patch or upgrade to a version of the FreePBX API module where the vulnerability is fixed by sanitizing shell command arguments using escapeshellarg(), as implemented in commit 5f194e3.

If patching immediately is not possible, consider temporarily disabling the vulnerable GraphQL moduleOperations mutation or restricting API access via firewall rules.

• Upgrade FreePBX API module to a version including the fix from commit 5f194e3.
• Restrict API access to trusted networks and users.
• Rotate and revoke any potentially compromised bearer tokens.
• Monitor logs for suspicious GraphQL mutation requests and unusual shell command executions.

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