CVE-2018-5191 in pfSense
Summary
by MITRE
/usr/local/www/csrf/csrf-magic.php in the WebGUI in pfSense before 2.4.2-RELEASE allows Clickjacking on the CSRF error page because the error detection occurs before an X-Frame-Options header is set.
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Analysis
by VulDB Data Team • 12/19/2019
The vulnerability identified as CVE-2018-5191 affects pfSense versions prior to 2.4.2-RELEASE and resides within the WebGUI component at /usr/local/www/csrf/csrf-magic.php. This issue represents a clickjacking vulnerability that undermines the security of the Cross-Site Request Forgery protection mechanism. The flaw occurs when the system processes CSRF error detection before establishing proper security headers, creating an exploitable condition that allows attackers to embed the vulnerable CSRF error page within malicious frames.
The technical implementation of this vulnerability stems from the improper ordering of security header application within the pfSense WebGUI framework. When a CSRF attack is detected, the system first processes the error detection logic and then attempts to set the X-Frame-Options header. This sequence creates a window where the error page can be rendered within an iframe, enabling attackers to perform clickjacking attacks against users who encounter CSRF errors. The vulnerability directly relates to CWE-1021, which describes improper handling of frame options and the failure to implement proper clickjacking protection mechanisms.
The operational impact of this vulnerability extends beyond simple CSRF protection failure, as it enables attackers to manipulate user interactions through malicious framing techniques. An attacker could craft a deceptive webpage that displays the legitimate pfSense CSRF error page within a hidden iframe, while overlaying transparent buttons or links that perform unintended actions when users interact with the malicious page. This creates a scenario where users might unknowingly execute administrative commands or submit sensitive information through the framed interface, effectively bypassing the intended CSRF protection measures.
The security implications of this vulnerability align with ATT&CK technique T1203, which describes exploitation of web application vulnerabilities for privilege escalation through user interaction. The vulnerability also demonstrates characteristics of T1557, which covers credential access through manipulation of web application security headers. Organizations running affected pfSense versions face significant risk of unauthorized administrative actions, as the clickjacking vector allows attackers to perform operations that would normally require legitimate user authentication and authorization. This vulnerability particularly impacts network administrators who rely on pfSense for firewall management and security policy enforcement.
The recommended mitigation strategy involves upgrading to pfSense 2.4.2-RELEASE or later versions where the proper header ordering has been implemented. Administrators should also ensure that all web applications implement consistent security header policies, with X-Frame-Options headers being set before any content is rendered. Additional protective measures include implementing Content Security Policy headers, regularly auditing web application security configurations, and conducting security assessments to identify similar header ordering issues in other components. Network security teams should monitor for exploitation attempts and maintain updated threat intelligence regarding clickjacking attacks targeting pfSense installations.