CVE-2018-18732 in AC7
Summary
by MITRE
An issue was discovered on Tenda AC7 V15.03.06.44_CN, AC9 V15.03.05.19(6318)_CN, AC10 V15.03.06.23_CN, AC15 V15.03.05.19_CN, and AC18 V15.03.05.19(6318)_CN devices. There is a buffer overflow vulnerability in the router's web server -- httpd. While processing the 'ntpServer' parameter for a post request, the value is directly used in a strcpy to a local variable placed on the stack, which overrides the return address of the function.
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Analysis
by VulDB Data Team • 04/07/2020
This vulnerability exists within the Tenda wireless router firmware versions AC7 V15.03.06.44_CN, AC9 V15.03.05.19(6318)_CN, AC10 V15.03.06.23_CN, AC15 V15.03.05.19_CN, and AC18 V15.03.05.19(6318)_CN, representing a critical buffer overflow flaw in the embedded web server component known as httpd. The vulnerability manifests when the router processes POST requests containing the ntpServer parameter, which is directly passed to a strcpy function without proper bounds checking. This fundamental programming error creates an exploitable condition where an attacker can manipulate the input to overflow the allocated stack buffer, thereby overwriting the function's return address and potentially gaining arbitrary code execution privileges on the affected device. The flaw aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of unsafe string handling in embedded systems. The impact extends beyond simple denial of service as this vulnerability enables remote code execution, allowing attackers to fully compromise the router's operational integrity. The exploitation requires sending a specially crafted POST request to the router's web interface, making it particularly dangerous as it can be executed remotely without authentication. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation. The affected devices operate with default administrative credentials, which significantly increases the attack surface as attackers can leverage this vulnerability to gain unauthorized access to network infrastructure. The buffer overflow occurs in the httpd web server process, which runs with elevated privileges, meaning successful exploitation could provide attackers with complete control over the router's network functions including DNS redirection, traffic interception, and potential lateral movement within the network. Network security professionals should note that this vulnerability affects a wide range of Tenda routers, making it particularly concerning for enterprise environments where these devices are commonly deployed. The lack of input validation and the use of dangerous functions like strcpy without proper bounds checking represents a common pattern in embedded firmware development where security considerations are often secondary to functionality. Remediation efforts should focus on updating firmware to versions that properly validate input parameters and implement proper bounds checking before string operations. The vulnerability demonstrates the critical importance of secure coding practices in embedded systems, particularly regarding memory management and input validation, as these devices often serve as gateways to larger network infrastructures and require robust security measures to prevent unauthorized access and potential data breaches. Organizations should conduct immediate vulnerability assessments to identify affected devices and implement network segmentation to limit potential exploitation. The long-term solution involves comprehensive firmware security reviews and implementation of automated security testing during development cycles to prevent similar vulnerabilities from being introduced in future releases.