CVE-2026-111226 in pfSense
Summary
by MITRE • 10/15/2026
pfSense CE 2.4.5 through 2.9.0 contains an OS command injection vulnerability that allows authenticated WebGUI users with Advanced Admin Access privilege to execute commands as root via Login Protection settings. Attackers can submit sshguard threshold, block time, or detection time values containing newlines or $(...) that are written unvalidated to sshguard.conf and sourced as root on restart.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in pfSense Community Edition versions 2.4.5 through 2.9.0 represents a critical OS command injection flaw located within the WebGUI interface, specifically affecting components related to Login Protection settings. This security defect allows authenticated users who possess Advanced Admin Access privileges to execute arbitrary operating system commands with root-level permissions. The core of the issue lies in the insufficient validation and sanitization of user-supplied input fields when configuring sshguard parameters such as threshold limits, block durations, or detection times. When an administrator submits these values through the web interface, the backend scripts write them directly into the sshguard configuration file without performing adequate checks for malicious payloads.
The technical mechanism of exploitation relies on the injection of special shell characters, specifically newlines and command substitution sequences denoted by dollar signs followed by parentheses. Because the input is written unvalidated to the sshguard.conf file, an attacker can craft a value that breaks out of the intended configuration parameter context. For instance, injecting a newline character allows the insertion of additional commands on subsequent lines within the configuration file. Alternatively, using command substitution syntax enables the execution of arbitrary shell commands inline with the configuration data. These malicious inputs are not merely stored; they become active when the system processes the configuration changes.
The operational impact is severe due to the privilege escalation inherent in how pfSense handles service restarts and configuration reloads. When the affected settings are applied, the system sources the sshguard.conf file as the root user to apply the new security policies. This sourcing action effectively executes any injected commands within a privileged shell context. Consequently, an attacker with Advanced Admin Access can achieve full control over the underlying operating system without needing higher-level credentials or exploiting separate vulnerabilities. This capability allows for complete compromise of the firewall appliance, including potential lateral movement into internal networks, data exfiltration, and persistence mechanisms that are difficult to detect due to their integration into legitimate configuration files.
This vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in an OS command, commonly known as OS Command Injection. The attack vector is classified under MITRE ATT&CK technique T1059, specifically subtechnique T1059.004 for Unix Shell Commands, and falls within the privilege escalation category due to the elevation from a standard administrative role to root access via configuration file manipulation. The flaw highlights the risks associated with sourcing untrusted or poorly validated input in system administration tools that operate with elevated privileges.
Mitigation strategies should prioritize immediate patching of pfSense CE to version 2.9.1 or later, where this issue has been addressed through improved input validation and sanitization routines. In environments where upgrading is not immediately feasible, administrators should restrict Advanced Admin Access to only those users who absolutely require it, thereby reducing the attack surface for potential exploitation. Additionally, implementing strict network segmentation can limit the impact of a compromised firewall by preventing lateral movement from the pfSense appliance into sensitive internal segments. Regular auditing of configuration files and monitoring for unusual shell activity during service restarts can also aid in early detection of such injection attempts.