CVE-2018-18729 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 heap-based buffer overflow vulnerability in the router's web server -- httpd. While processing the 'mac' parameter for a post request, the value is directly used in a strcpy to a variable placed on the heap, which can leak sensitive information or even hijack program control flow.
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Analysis
by VulDB Data Team • 04/07/2020
This vulnerability exists in multiple Tenda router models including AC7, AC9, AC10, AC15, and AC18 running specific firmware versions. The issue resides within the web server component known as httpd which handles incoming http requests from connected clients. The vulnerability manifests when the router processes post requests containing a 'mac' parameter, creating a critical heap-based buffer overflow condition that can be exploited by remote attackers. The flaw occurs because the system directly copies user-supplied data from the 'mac' parameter into a heap-allocated buffer without proper bounds checking or validation. This primitive strcpy operation lacks input sanitization and size verification, allowing maliciously crafted input to exceed the allocated buffer boundaries and overwrite adjacent memory locations.
The technical execution of this vulnerability follows a classic heap overflow pattern where the vulnerable code path processes user input through a web interface without adequate memory safety mechanisms. When an attacker sends a specially crafted post request with an excessively long mac parameter value, the strcpy function writes beyond the intended buffer boundaries into adjacent heap memory. This memory corruption can result in information disclosure through heap content leakage or more severe exploitation possibilities including arbitrary code execution. The heap-based nature of the vulnerability means that the overflow affects dynamically allocated memory segments rather than stack-based buffers, making it particularly challenging to predict and prevent. According to CWE classification, this represents a CWE-121 heap-based buffer overflow vulnerability, which falls under the broader category of CWE-787 out-of-bounds write conditions that can lead to system compromise.
The operational impact of this vulnerability extends beyond simple data leakage, as it provides potential attackers with pathways to gain unauthorized control over affected router devices. Successful exploitation could enable attackers to execute arbitrary code with the privileges of the httpd process, potentially allowing full router compromise and subsequent network infiltration. The vulnerability affects the core web management interface of these routers, meaning that any attacker with network access could potentially exploit this without requiring physical access to the device. This creates a significant risk for enterprise and home network environments where these devices are commonly deployed. The exposure of sensitive memory contents through information leakage could reveal system internals, credentials, or other confidential data that might aid in further attacks. According to ATT&CK framework, this vulnerability maps to T1210 - Exploitation of Remote Services and T1059 - Command and Scripting Interpreter, as it enables remote code execution through web service exploitation.
Mitigation strategies for this vulnerability should focus on immediate firmware updates from Tenda to address the buffer overflow condition in the httpd web server component. Network administrators should implement strict firewall rules to limit external access to router management interfaces and consider disabling web management services when not actively needed. The implementation of input validation and bounds checking mechanisms within the affected web server code would prevent the strcpy operations from writing beyond allocated buffer boundaries. Additionally, deploying intrusion detection systems that monitor for anomalous post request patterns containing oversized mac parameters could help detect exploitation attempts. Regular security audits of router firmware and network device configurations should be conducted to identify similar vulnerabilities in other network infrastructure components. Organizations should also consider network segmentation and zero-trust security models to limit the potential impact of successful exploitation attempts, ensuring that even if one device is compromised, attackers cannot easily pivot to other network segments.