CVE-2018-18709 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 "firewallEn" 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 in multiple Tenda wireless router models including AC7, AC9, AC10, AC15, and AC18, all running specific firmware versions. The issue stems from a critical buffer overflow flaw within the httpd web server component that handles incoming POST requests. The vulnerability manifests when the router processes the "firewallEn" parameter, which is passed through HTTP POST requests to the web interface. This particular parameter triggers a dangerous code path where user-supplied input is directly copied into a local stack buffer without proper bounds checking, creating an exploitable condition that can be leveraged by remote attackers.
The technical implementation of this vulnerability follows a classic stack-based buffer overflow pattern where the strcpy function is used to copy the "firewallEn" parameter value into a local variable allocated on the stack. This direct copying without size validation allows an attacker to overflow the allocated buffer space and overwrite adjacent memory locations, specifically targeting the return address of the calling function. The stack-based nature of this vulnerability means that attackers can precisely control the overwritten return address, enabling them to redirect program execution to arbitrary code locations. This type of vulnerability is categorized under CWE-121 Stack-based Buffer Overflow, which represents a fundamental memory safety issue in C programming where buffer boundaries are not properly enforced.
The operational impact of this vulnerability is severe as it provides remote code execution capabilities to authenticated attackers who can manipulate the router's web interface. An attacker could potentially gain full administrative control over the affected devices, allowing them to modify firewall settings, access network traffic, change router configurations, or even install malicious firmware. The vulnerability affects multiple router models across different product lines, amplifying the potential attack surface and making it a widespread concern for network administrators managing Tenda devices. Additionally, since the vulnerability exists in the web server component, attackers do not require physical access to the device or specialized network reconnaissance to exploit it, making it particularly dangerous in enterprise and residential network environments.
The exploitation of this vulnerability aligns with several techniques documented in the ATT&CK framework, specifically targeting the T1059.007 command and scripting interpreter and T1078 valid accounts categories. The ability to execute arbitrary code through web interface manipulation represents a significant compromise of the device's security posture, enabling attackers to establish persistent access and potentially use the compromised router as a foothold for further network infiltration. Network defenders should consider implementing network segmentation and monitoring for unusual traffic patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of firmware security updates and proper input validation practices in embedded systems, as this type of issue is preventable through defensive programming techniques such as using safer string functions like strncpy or implementing proper bounds checking mechanisms. Organizations should prioritize immediate firmware updates from Tenda to address this vulnerability and conduct thorough network assessments to identify any potential exploitation attempts or compromised devices within their infrastructure.