CVE-2026-111221 in pfSense
Summary
by MITRE • 10/15/2026
Netgate pfSense CE through 2.9.0 contains a configuration injection vulnerability that allows authenticated WebGUI users to inject mpd5 commands by submitting an unescaped RADIUS shared secret. Attackers with L2TP or PPPoE Server edit privileges can POST a secret containing a quote and newline to vpn_l2tp.php or services_pppoe_edit.php, appending an up-script that executes as root when a session starts.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in Netgate pfSense Community Edition versions through 2.9.0 represents a critical configuration injection flaw within the WebGUI interface. This security defect specifically targets authenticated users who possess edit privileges for L2TP or PPPoE server configurations. The core technical issue stems from insufficient input validation and sanitization of the RADIUS shared secret field during POST requests to vpn_l2tp.php or services_pppoe_edit.php. When an attacker submits a maliciously crafted string containing unescaped quotes and newline characters, the system fails to properly escape these inputs before passing them to underlying configuration scripts. This lack of proper encoding allows the injected payload to break out of its intended context within the configuration file structure.
The operational impact of this vulnerability is severe due to the execution environment of the affected components. The injected commands are processed by mpd5, a multi-link Point-to-Point Protocol daemon that runs with root privileges on the pfSense system. By injecting an up-script via the RADIUS shared secret field, an attacker can cause arbitrary code execution as the root user whenever a new L2TP or PPPoE session is established. This effectively grants full control over the firewall appliance to any authenticated user with the specified edit permissions. The ability to execute commands at this privilege level allows for complete compromise of the network infrastructure, including potential pivoting to other internal systems, data exfiltration, and persistent backdoor installation.
From a classification perspective, this vulnerability aligns closely with CWE-94 Improper Control of Generation of Code or Command Injection, as it involves the injection of executable code into a system command context through unsanitized user input. Furthermore, in terms of tactical mapping within the MITRE ATT&CK framework, this exploit technique corresponds to T1505.003 Server Message Block (SMB) Events and potentially T1496 Remote Service Exploitation if leveraged for lateral movement after initial access. The attack vector relies on authenticated interaction with a web-based management interface, highlighting the risk associated with privileged administrative interfaces even when accessed by legitimate but compromised or malicious internal users.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary defense is to apply the vendor-provided patch that updates pfSense CE to version 2.9.1 or later, which addresses the input validation flaws in the RADIUS configuration handling. In environments where patching is not immediately feasible, administrators should restrict WebGUI access using strong network segmentation and multi-factor authentication to limit exposure to authenticated users with edit privileges. Additionally, implementing strict role-based access control (RBAC) ensures that only essential personnel have permissions to modify VPN server configurations. Regular auditing of user activity logs within the pfSense interface can also help detect suspicious POST requests indicative of exploitation attempts before significant damage occurs.