CVE-2018-13380 in FortiOS
Summary
by MITRE
A Cross-site Scripting (XSS) vulnerability in Fortinet FortiOS 6.0.0 to 6.0.4, 5.6.0 to 5.6.7, 5.4 and below versions under SSL VPN web portal allows attacker to execute unauthorized malicious script code via the error or message handling parameters.
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Analysis
by VulDB Data Team • 09/26/2023
This cross-site scripting vulnerability exists within Fortinet FortiOS SSL VPN web portal functionality across multiple affected versions including 6.0.0 through 6.0.4, 5.6.0 through 5.6.7, and all 5.4 and earlier releases. The flaw specifically manifests in the error and message handling parameters of the web portal interface, creating a pathway for malicious actors to inject unauthorized script code into the application's response handling mechanisms. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, which represents one of the most prevalent and dangerous web application security flaws in the industry. The attack vector leverages the improper sanitization of user-supplied input within the error message processing components, allowing attackers to craft malicious payloads that execute in the context of authenticated users' browsers. The vulnerability is particularly concerning because it operates within the SSL VPN portal environment where users typically have elevated privileges and access to corporate networks, making the potential impact significantly greater than standard web application XSS flaws.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious input parameters that are subsequently reflected or stored within the error or message handling sections of the SSL VPN web portal. When legitimate users interact with the vulnerable system and encounter error messages or system notifications, the malicious script code embedded within the parameters executes in their browser context. This creates a persistent threat where attackers can establish malicious sessions, steal session cookies, perform unauthorized actions on behalf of users, or redirect victims to phishing sites. The vulnerability's impact extends beyond simple script execution as it can be leveraged for session hijacking, privilege escalation, and data exfiltration attacks. The weakness demonstrates poor input validation and output encoding practices that violate fundamental web security principles and aligns with ATT&CK technique T1059.001 for command and scripting interpreter usage, as the malicious code can execute commands within the victim's browser environment.
The operational impact of this vulnerability is substantial for organizations utilizing affected Fortinet FortiOS versions, particularly those with extensive SSL VPN deployments. Attackers can exploit this flaw to gain unauthorized access to corporate resources, potentially compromising sensitive data and network infrastructure. The vulnerability affects organizations that rely on SSL VPN for remote access, making it a critical concern for enterprises with distributed workforces. The risk is amplified by the fact that the vulnerability exists in error handling mechanisms, meaning that even routine system errors or user input validation failures could provide attack vectors. Organizations may experience unauthorized access to internal systems, data breaches, and potential lateral movement within their network. The vulnerability's presence in multiple version lines indicates a widespread issue that requires immediate attention from security teams. The impact is further compounded by the fact that the attack can be executed without authentication, making it particularly dangerous as attackers can exploit the flaw even when they do not possess valid credentials. This vulnerability can serve as a stepping stone for more sophisticated attacks, including privilege escalation and persistent access within the network infrastructure.
Organizations should immediately implement mitigation strategies including applying the latest Fortinet security patches and firmware updates to address the vulnerability. The recommended approach involves upgrading to FortiOS versions that contain the necessary security fixes, specifically versions that have addressed the XSS flaw in the SSL VPN portal error handling components. Network administrators should also consider implementing web application firewalls to filter malicious input and monitor for suspicious traffic patterns that may indicate exploitation attempts. Input validation should be strengthened across all web portal components, with particular attention to error message handling and parameter processing. Security teams should conduct thorough vulnerability assessments to identify any other potentially affected systems within their environment. The implementation of Content Security Policy headers can provide additional protection against script execution, though this should be considered a supplementary measure rather than a primary defense. Regular security monitoring and log analysis should be enhanced to detect potential exploitation attempts, with particular focus on SSL VPN access logs and error message patterns. Organizations should also review their incident response procedures to ensure preparedness for potential exploitation of this vulnerability, as the nature of XSS attacks can lead to various forms of compromise including session hijacking and data exfiltration.