CVE-2021-45737 in A720R
Summary
by MITRE • 02/04/2022
TOTOLINK A720R v4.1.5cu.470_B20200911 was discovered to contain a stack overflow in the Form_Login function. This vulnerability allows attackers to cause a Denial of Service (DoS) via the Host parameter.
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Analysis
by VulDB Data Team • 02/05/2022
The vulnerability identified as CVE-2021-45737 affects the TOTOLINK A720R router firmware version v4.1.5cu.470_B20200911 and represents a critical stack overflow condition within the Form_Login function. This type of vulnerability falls under the CWE-121 stack-based buffer overflow category, where insufficient bounds checking allows an attacker to overwrite adjacent memory locations on the program stack. The specific exploitation vector targets the Host parameter, which suggests that the router's web interface processes this parameter without adequate input validation or sanitization before passing it to memory operations that assume a certain buffer size.
The technical flaw manifests when an attacker crafts a malicious Host parameter value that exceeds the allocated stack buffer size, causing a stack overflow condition that typically results in program termination or unpredictable behavior. This vulnerability directly enables a denial of service attack scenario where an adversary can disrupt legitimate network services by sending specifically crafted requests to the router's web management interface. The stack overflow occurs during the login form processing, indicating that the vulnerability exists in the authentication handling code path, which is particularly concerning as it could potentially be exploited to bypass authentication mechanisms or escalate privileges.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a foundational security weakness that could be leveraged by attackers to gain unauthorized access to the network infrastructure. Network administrators and security professionals should recognize this as a significant risk to enterprise and home network security, particularly in environments where these devices serve as primary network gateways. The vulnerability demonstrates poor input validation practices in web application development and highlights the importance of implementing proper bounds checking and memory management protocols in embedded systems. Attackers could potentially exploit this condition to cause persistent service outages or create opportunities for more sophisticated attacks that might otherwise be blocked by standard security measures.
Mitigation strategies for CVE-2021-45737 should include immediate firmware updates from TOTOLINK to address the stack overflow condition in the Form_Login function. Network administrators should also implement network segmentation to limit exposure of these devices to untrusted networks and consider disabling unnecessary web management interfaces when possible. The vulnerability aligns with ATT&CK technique T1210 for exploiting vulnerabilities in remote services and T1499 for denial of service attacks, making it particularly relevant for organizations implementing threat hunting and incident response procedures. Additionally, implementing web application firewalls and input validation rules specifically targeting long parameter values in the Host header can provide temporary protection while permanent fixes are deployed. Organizations should also conduct vulnerability assessments to identify other potentially affected devices running similar firmware versions and ensure that all networked devices receive timely security updates to prevent exploitation of similar stack overflow conditions.