CVE-2019-16667 in pfSense
Summary
by MITRE
diag_command.php in pfSense 2.4.4-p3 allows CSRF via the txtCommand or txtRecallBuffer field, as demonstrated by executing OS commands. This occurs because csrf_callback() produces a "CSRF token expired" error and a Try Again button when a CSRF token is missing.
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Analysis
by VulDB Data Team • 09/08/2025
The vulnerability identified as CVE-2019-16667 affects pfSense version 2.4.4-p3 and resides within the diag_command.php script which handles diagnostic command execution functionality. This represents a critical cross-site request forgery vulnerability that enables attackers to execute arbitrary operating system commands on affected systems without proper authentication. The flaw specifically targets the txtCommand and txtRecallBuffer input fields, which are processed through the csrf_callback() function that manages cross-site request forgery protection mechanisms. When a CSRF token is missing or expired, the system responds with a "CSRF token expired" error message and displays a "Try Again" button, indicating that the application's security controls are insufficient to prevent unauthorized command execution.
The technical implementation of this vulnerability stems from improper validation of CSRF tokens within the diagnostic command execution interface. The csrf_callback() function, which should enforce strict token validation and prevent unauthorized requests, fails to adequately protect against forged requests that bypass the expected security controls. This weakness allows attackers to craft malicious requests that appear legitimate to the pfSense system but are actually submitted by unauthorized parties. The vulnerability operates under CWE-352, which specifically addresses Cross-Site Request Forgery issues in software applications. Attackers can leverage this flaw by constructing specially crafted web pages or emails that, when visited by an authenticated user, automatically submit commands to the pfSense system through the vulnerable diag_command.php endpoint.
The operational impact of this vulnerability is severe and far-reaching for pfSense administrators and network security teams. An attacker who successfully exploits this CSRF vulnerability can execute arbitrary OS commands with the privileges of the web application user, typically root or a high-privilege account. This compromise enables full system control including but not limited to command execution, file manipulation, network configuration changes, and potential lateral movement within the network. The vulnerability essentially provides a backdoor for attackers to gain complete administrative control over the affected pfSense firewall appliance, potentially compromising the entire network security infrastructure that relies on the device for traffic filtering and security enforcement.
Organizations using pfSense 2.4.4-p3 should immediately implement mitigations including applying the vendor-provided security patches that address the CSRF token validation issues. The recommended remediation approach involves ensuring that all input fields in the diag_command.php script properly validate CSRF tokens before processing any command execution requests. Security teams should also implement additional defensive measures such as network segmentation, web application firewalls, and monitoring for suspicious command execution patterns. From an ATT&CK framework perspective, this vulnerability maps to technique T1059.001 for command and scripting interpreter, and T1566 for phishing with malicious attachments or links. The mitigation strategy should also include user education to avoid clicking suspicious links that might trigger CSRF attacks, along with regular security audits of web application interfaces to identify similar vulnerabilities that could be exploited for privilege escalation or system compromise.