CVE-2018-18707 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. It is a buffer overflow vulnerability in the router's web server -- httpd. When processing the "ssid" 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 represents a critical buffer overflow flaw in the Tenda router firmware affecting multiple models including AC7 AC9 AC10 AC15 and AC18 devices. The vulnerability exists within the httpd web server component that handles incoming post requests and specifically processes the ssid parameter without proper input validation. The flaw occurs when the router's web server receives a maliciously crafted ssid parameter in a post request and directly copies this input into a local stack buffer using the unsafe strcpy function. This primitive operation lacks bounds checking and allows an attacker to overflow the allocated buffer space, which subsequently overwrites the function's return address on the stack. The vulnerability directly maps to CWE-121 which describes stack-based buffer overflow conditions where insufficient boundary checking allows attackers to overwrite adjacent memory locations including return addresses and other critical program state information. This type of vulnerability provides attackers with the opportunity to execute arbitrary code on the affected devices through stack-based buffer overflow exploitation techniques.
The operational impact of this vulnerability extends beyond simple denial of service scenarios as it enables remote code execution capabilities that can be leveraged for complete system compromise. Attackers can craft malicious post requests containing overly long ssid parameter values that trigger the buffer overflow condition, allowing them to overwrite the return address and redirect execution flow to malicious code injected into the stack. Once successfully exploited, attackers gain unauthorized access to the router's administrative functions and can potentially establish persistent backdoors within the network infrastructure. The vulnerability affects firmware versions V15.03.06.44_CN through V15.03.05.19(6318)_CN across multiple router models, indicating a widespread issue that could impact numerous network devices deployed in both residential and enterprise environments. Network administrators should consider this vulnerability as a high-priority threat under the MITRE ATT&CK framework's T1059.007 technique which covers command and scripting interpreter usage and potentially T1071.004 for application layer protocols involving web services.
Mitigation strategies should focus on immediate firmware updates from Tenda's official sources to address the root cause of the buffer overflow vulnerability. Organizations should implement network segmentation and access controls to limit exposure of these devices to untrusted networks while monitoring for suspicious post requests that might indicate exploitation attempts. Network administrators should also consider implementing intrusion detection systems capable of identifying malformed ssid parameters that exceed normal length thresholds and could indicate exploitation attempts. The vulnerability highlights the importance of proper input validation and the use of safer string manipulation functions such as strlcpy or strncpy instead of the vulnerable strcpy function. Additionally, implementing address space layout randomization ASLR and stack canaries can provide additional defense-in-depth measures against exploitation attempts. Regular security audits of network infrastructure components and maintaining up-to-date firmware repositories should be standard practices to prevent similar vulnerabilities from compromising network security. The affected devices should be isolated from critical network segments until confirmed patched and the vulnerability should be monitored against potential exploit development by threat actors.