CVE-2015-3626 in FortiOS
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the DHCP Monitor page the Web User Interface (WebUI) in Fortinet FortiOS before 5.2.4 on FortiGate devices allows remote attackers to inject arbitrary web script or HTML via a crafted hostname.
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Analysis
by VulDB Data Team • 03/07/2018
The vulnerability identified as CVE-2015-3626 represents a critical cross-site scripting flaw within the Web User Interface of Fortinet FortiOS versions prior to 5.2.4. This issue specifically affects the DHCP Monitor page functionality of FortiGate devices, creating a significant security risk that enables remote attackers to execute malicious web scripts or HTML code within the context of authenticated user sessions. The vulnerability stems from inadequate input validation and sanitization mechanisms within the web interface's handling of hostname parameters, allowing attackers to inject malicious payloads through carefully crafted hostnames that are then rendered in the DHCP Monitor page without proper encoding or filtering.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious hostname containing embedded script code and submits it through the DHCP monitoring interface. The FortiOS web application fails to properly sanitize or encode this input before displaying it in the user interface, resulting in the execution of the injected script within the browser context of any user who views the affected DHCP Monitor page. This type of vulnerability falls under CWE-79, which specifically addresses Cross-Site Scripting flaws in web applications, and aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments or links. The flaw demonstrates poor input validation practices and inadequate output encoding, creating a persistent security weakness that can be exploited across multiple user sessions and potentially escalate to more severe attack vectors.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform session hijacking, steal sensitive authentication tokens, or redirect users to malicious websites. Remote attackers can leverage this weakness to gain unauthorized access to the FortiGate device management interface, potentially leading to complete compromise of the network security infrastructure. The attack surface is particularly concerning given that FortiGate devices serve as critical network security appliances, and successful exploitation could allow attackers to view sensitive network configurations, modify security policies, or establish persistent access points within the network. This vulnerability can be exploited by unauthenticated attackers who simply need to submit a malicious hostname through the DHCP monitoring interface, making it a particularly dangerous flaw that affects the fundamental security posture of affected organizations.
Mitigation strategies for CVE-2015-3626 require immediate deployment of Fortinet FortiOS version 5.2.4 or later, which includes proper input sanitization and output encoding mechanisms to prevent XSS injection attacks. Organizations should also implement network segmentation and access controls to limit exposure of the web interface to trusted networks only, while monitoring for suspicious hostname entries in DHCP logs. Security teams should conduct comprehensive vulnerability assessments of their FortiGate deployments and ensure that all administrative interfaces are properly secured through multi-factor authentication and secure remote access protocols. Additionally, regular security updates and patch management processes should be enforced to maintain protection against similar vulnerabilities, while implementing web application firewalls to detect and block suspicious input patterns that may attempt to exploit similar XSS weaknesses in other components of the network infrastructure.