CVE-2021-3304 in F@ST 3686 v2
Summary
by MITRE • 01/26/2021
Sagemcom F@ST 3686 v2 3.495 devices have a buffer overflow via a long sessionKey to the goform/login URI.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 02/20/2021
The Sagemcom FST 3686 v2 3.495 router firmware contains a critical buffer overflow vulnerability located within the web-based administration interface. This flaw exists in the handling of sessionKey parameters submitted to the goform/login URI endpoint, where the device fails to properly validate input length before processing user authentication requests. The vulnerability stems from insufficient bounds checking in the session management subsystem, allowing an attacker to craft malicious requests that exceed the allocated buffer space. This particular implementation flaw represents a classic stack-based buffer overflow condition that can be exploited through crafted HTTP requests targeting the login form interface. The vulnerability affects all devices running firmware version 3.495 and potentially earlier versions of the FST 3686 v2 series, making it a widespread concern for network administrators managing these devices.
The technical exploitation of this buffer overflow vulnerability follows established patterns that align with CWE-121 Stack-based Buffer Overflow, where insufficient input validation allows attackers to overwrite adjacent memory locations. When a maliciously long sessionKey is submitted to the goform/login URI, the device's web server processes the input without proper boundary checks, causing the stack to overflow and potentially allowing arbitrary code execution. This vulnerability can be leveraged by remote attackers without requiring authentication, as the buffer overflow occurs during the login process itself, making it particularly dangerous for devices accessible from the internet. The attack surface extends beyond simple denial of service to include potential privilege escalation and complete system compromise, as the overflow may allow an attacker to overwrite critical program execution pointers or inject malicious code into the running process. The vulnerability demonstrates poor input validation practices that violate fundamental security principles and represents a failure to implement proper bounds checking mechanisms.
The operational impact of this vulnerability extends far beyond simple exploitation, as it creates a significant risk for network infrastructure security. Organizations with unpatched Sagemcom F@ST 3686 v2 devices face potential unauthorized access to their network configurations, allowing attackers to modify routing tables, disable security features, or establish persistent backdoors. The remote nature of the exploit means that attackers can target these devices from anywhere on the internet without requiring physical access or local network presence. This vulnerability directly maps to ATT&CK technique T1210 Exploitation of Remote Services, as it exploits a service running on the device's web interface. The compromise of these devices can lead to larger network infiltration campaigns, as routers often serve as central points of control and may provide access to internal network resources. Additionally, the vulnerability could enable attackers to perform man-in-the-middle attacks, DNS hijacking, or other advanced persistent threats that leverage the router's privileged position within the network topology.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security improvements. The most critical action is to update all affected devices to firmware versions that contain proper input validation and buffer overflow protections. Organizations should implement network segmentation to isolate critical devices and monitor for anomalous traffic patterns that might indicate exploitation attempts. Network administrators should disable unnecessary services and ensure that only authorized users can access the web administration interface. Regular security audits should include verification of device firmware versions and implementation of proper input sanitization practices. The vulnerability highlights the importance of implementing secure coding practices such as those recommended in the OWASP Secure Coding Practices and the CERT Secure Coding Standards, particularly regarding input validation and memory management. Organizations should also consider implementing intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability and establish incident response procedures for handling potential compromises of network infrastructure devices.