CVE-2021-43064 in FortiWeb
Summary
by MITRE • 12/08/2021
A url redirection to untrusted site ('open redirect') in Fortinet FortiWeb version 6.4.1 and 6.4.0, version 6.3.15 and below, version 6.2.6 and below allows attacker to use the device as a proxy and reach external or protected hosts via redirection handlers.
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Analysis
by VulDB Data Team • 10/27/2024
The vulnerability identified as CVE-2021-43064 represents a critical open redirect flaw within Fortinet FortiWeb web application firewalls, specifically affecting versions 6.4.1 and 6.4.0, 6.3.15 and below, and 6.2.6 and below. This security weakness enables attackers to manipulate the redirection functionality of the FortiWeb appliance to direct users to malicious external domains, effectively exploiting the device's inherent trust mechanisms to facilitate unauthorized access patterns. The flaw fundamentally undermines the security posture of organizations relying on FortiWeb for web application protection and network security enforcement.
The technical implementation of this vulnerability stems from insufficient input validation within FortiWeb's redirection handlers, allowing crafted URLs containing malicious redirect parameters to bypass security controls and establish unauthorized communication pathways. When users interact with compromised redirection endpoints, the appliance processes these requests without adequate verification of destination domains, creating opportunities for attackers to leverage the device as an intermediary for reaching internal or protected network resources. This behavior aligns with CWE-601 vulnerability classification, specifically addressing open redirect issues where applications fail to validate redirect targets, and corresponds to ATT&CK technique T1071.004 for application layer protocol: DNS, demonstrating how attackers can manipulate application behavior to achieve unauthorized network access.
The operational impact of this vulnerability extends beyond simple redirection attacks, as it enables sophisticated attack patterns including credential theft, data exfiltration, and lateral movement within network environments. Attackers can construct malicious URLs that appear legitimate to users while directing traffic through the FortiWeb appliance to reach internal systems that would otherwise be protected by the firewall's security policies. This capability transforms the FortiWeb device from a protective security layer into a potential attack vector, allowing threat actors to bypass network segmentation controls and access sensitive resources that should remain isolated from external exposure. The vulnerability particularly affects organizations with complex network architectures where FortiWeb serves as a critical security gateway for web traffic management.
Mitigation strategies for CVE-2021-43064 require immediate implementation of firmware updates from Fortinet to address the specific redirection validation flaws present in affected versions. Organizations should also implement network-level restrictions to prevent unauthorized access to FortiWeb management interfaces and establish monitoring procedures to detect anomalous redirection patterns. Security teams should conduct comprehensive vulnerability assessments to identify all instances of affected FortiWeb appliances within their infrastructure and apply the appropriate security patches as released by Fortinet. Additional defensive measures include implementing strict URL validation policies, configuring access controls to limit redirection functionality, and establishing network segmentation strategies that minimize the potential impact of compromised redirection handlers. The vulnerability demonstrates the critical importance of maintaining up-to-date security appliances and implementing robust input validation controls to prevent attackers from exploiting seemingly minor functionality flaws to achieve significant security breaches.