CVE-2018-18730 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 'startIp' and 'endIp' parameters for a post request, each 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
The vulnerability identified as CVE-2018-18730 represents a critical buffer overflow flaw 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. This vulnerability exists in the web server component known as httpd which handles incoming post requests from web clients. The flaw manifests when the router processes network configuration parameters, specifically the 'startIp' and 'endIp' values that are commonly used in subnet configuration and IP range settings. The vulnerability stems from improper input validation and handling within the firmware's web interface processing logic, creating a scenario where maliciously crafted input can overwrite critical memory locations.
The technical implementation of this buffer overflow occurs through the direct usage of user-supplied parameters in a sprintf function call without proper bounds checking or length validation. When the httpd web server receives a post request containing these parameters, it directly passes the 'startIp' and 'endIp' values to a sprintf operation targeting a local stack variable. This approach violates fundamental security principles and creates a predictable memory corruption scenario. The stack-based buffer overflow specifically targets the return address of the calling function, allowing an attacker to manipulate the program's execution flow. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and CWE-787, which covers out-of-bounds write vulnerabilities.
The operational impact of this vulnerability extends beyond simple denial of service, presenting significant security risks to affected Tenda router installations. An attacker who successfully exploits this buffer overflow could potentially execute arbitrary code on the affected device with the privileges of the httpd process, which typically runs with elevated system permissions. This remote code execution capability enables attackers to gain full control over the router, potentially allowing them to modify network configurations, redirect traffic, establish persistent backdoors, or use the compromised device as a pivot point for attacking other systems within the local network. The vulnerability's remote exploitability means attackers do not require physical access to the device, making it particularly dangerous for enterprise and residential networks alike.
The attack surface for this vulnerability is particularly concerning given that the affected routers are widely deployed in both home and small office environments. The exploit requires only a web browser and network connectivity to the affected device's management interface, making it accessible to threat actors with minimal technical expertise. From an ATT&CK framework perspective, this vulnerability maps to several techniques including T1059.007 for command and script interpreter execution, T1046 for network service scanning, and T1071.004 for application layer protocols. The vulnerability also represents a significant concern for the T1068 privilege escalation technique, as the compromised router could serve as a platform for further network infiltration. Organizations should consider implementing network segmentation, regular firmware updates, and monitoring for unusual network traffic patterns as part of their defensive strategy. The vulnerability underscores the importance of secure coding practices, particularly around input validation and memory management, as outlined in the OWASP Top 10 and NIST Cybersecurity Framework guidelines.