CVE-2018-18708 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 "page" parameter of the function "fromAddressNat" for a post request, the value is directly used in a sprintf 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 resides within the Tenda 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 processing POST requests containing the "page" parameter within the "fromAddressNat" function, creating a classic stack-based buffer overflow condition that directly compromises the router's execution flow.
The technical implementation of this flaw involves the direct usage of user-controllable input without proper bounds checking or sanitization within the sprintf function call. When the web server processes the maliciously crafted "page" parameter, the input data is copied directly into a local stack variable that is insufficiently sized to accommodate the potentially large input. This overflow condition allows an attacker to overwrite adjacent memory locations including the return address of the calling function, effectively enabling arbitrary code execution through controlled memory corruption.
From an operational perspective, this vulnerability presents a severe security risk as it allows remote attackers to achieve arbitrary code execution on affected router devices without requiring authentication. The implications extend beyond simple privilege escalation, as compromised routers can serve as entry points for broader network infiltration, enabling attackers to establish persistent backdoors, redirect traffic, or launch further attacks against connected devices. The stack-based nature of the overflow makes exploitation relatively straightforward compared to heap-based vulnerabilities, as attackers can directly control the return address and potentially jump to shellcode or existing code gadgets within the router's memory space.
The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions, and represents a clear violation of secure coding practices that should prevent such memory corruption issues. From an attack framework perspective, this vulnerability maps to multiple ATT&CK techniques including T1059 Command and Scripting Interpreter and T1071.004 Application Layer Protocol DNS, as successful exploitation could enable attackers to execute commands and potentially manipulate network traffic. The impact assessment reveals this vulnerability affects a significant number of consumer and small office routers, making it attractive to threat actors seeking to establish persistent network footholds. Mitigation strategies should include immediate firmware updates from Tenda, network segmentation to limit potential lateral movement, and implementation of intrusion detection systems to monitor for exploitation attempts. Network administrators should also consider disabling unnecessary web management interfaces and implementing proper access controls to minimize the attack surface of affected devices.