CVE-2015-6511 in pfSense
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in pfSense before 2.2.3 allows remote attackers to inject arbitrary web script or HTML via the server[] parameter to services_ntpd.php.
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Analysis
by VulDB Data Team • 10/18/2017
The CVE-2015-6511 vulnerability represents a critical cross-site scripting flaw discovered in pfSense versions prior to 2.2.3, specifically affecting the services_ntpd.php web interface component. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, which is classified as a fundamental web application security weakness that enables attackers to inject malicious client-side scripts into web pages viewed by other users. The vulnerability exists within the Network Time Protocol service configuration interface, making it particularly dangerous as it allows remote attackers to execute arbitrary web scripts or HTML code through a carefully crafted server[] parameter.
The technical exploitation of this vulnerability occurs when an attacker submits malicious input through the server[] parameter in the services_ntpd.php script, which fails to properly sanitize or validate user-supplied data before incorporating it into the web page output. This lack of input validation creates an environment where attacker-controlled content can be executed within the context of other users' browsers, potentially leading to session hijacking, credential theft, or redirection to malicious websites. The vulnerability is particularly concerning because it affects the core network time synchronization service configuration, which is frequently accessed by system administrators and network operators.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable sophisticated attack vectors including persistent XSS payloads that remain active until the web application is restarted or the affected page is refreshed. Attackers can leverage this weakness to establish backdoors, steal administrative sessions, or perform actions on behalf of authenticated users with elevated privileges. The vulnerability's remote nature means that attackers do not require physical access or local network presence to exploit it, making it particularly dangerous in environments where pfSense firewalls are exposed to untrusted networks. This weakness directly aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1566.001 for Phishing, as it enables the delivery of malicious payloads that can be executed in victim browsers.
Organizations using affected pfSense versions should immediately implement mitigations including updating to pfSense 2.2.3 or later, which contains the necessary patches to address this vulnerability. Network administrators should also consider implementing additional security controls such as web application firewalls, input validation rules, and regular security assessments of network infrastructure components. The vulnerability demonstrates the critical importance of keeping network security appliances updated, as these devices often serve as primary targets for attackers seeking to establish persistent access to network environments. Additionally, implementing proper input sanitization and output encoding practices in web applications can prevent similar vulnerabilities from occurring in other components of the system.