CVE-2018-18727 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 'deviceList' 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
The vulnerability identified as CVE-2018-18727 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 issue resides in the web server component known as httpd which handles incoming HTTP requests from network clients. The vulnerability manifests when the router processes POST requests containing a specifically crafted 'deviceList' parameter, creating a dangerous condition that allows remote attackers to manipulate the device's execution flow. The flaw stems from improper input validation where user-supplied data is directly copied into a local stack buffer without adequate bounds checking, violating fundamental security principles of memory safety and input sanitization.
The technical implementation of this vulnerability follows a classic stack-based buffer overflow pattern where the strcpy function is employed to copy the 'deviceList' parameter value into a fixed-size local buffer allocated on the stack. This copying operation lacks any size validation or boundary checking mechanisms, allowing an attacker to overflow the allocated buffer space and overwrite adjacent memory locations. The most critical consequence occurs when the return address of the function is overwritten, effectively allowing an attacker to redirect the execution flow of the httpd process. This manipulation of the return address enables arbitrary code execution within the context of the web server process, which typically runs with elevated privileges due to its role in managing router configuration and network services. The vulnerability maps directly to CWE-121 Stack-based Buffer Overflow, which is classified as a high-severity weakness in the Common Weakness Enumeration catalog, specifically addressing buffer overflows that occur in stack-based memory allocations.
The operational impact of this vulnerability extends far beyond simple denial of service conditions, presenting attackers with a pathway to achieve complete system compromise of affected Tenda routers. Remote exploitation allows unauthorized individuals to execute malicious code on the device, potentially leading to persistent backdoor access, data exfiltration, network reconnaissance, and further lateral movement within the compromised network. The web server component represents a primary attack surface since it accepts HTTP requests from external sources, making the vulnerability particularly dangerous in environments where routers are exposed to untrusted networks. Once successfully exploited, attackers can gain access to sensitive router configuration data, modify network settings, establish persistent access points, and potentially use the compromised device as a pivot point for attacking other systems within the local network. This vulnerability directly aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1071.004 for Application Layer Protocol, as it enables remote command execution through web-based interfaces.
Mitigation strategies for CVE-2018-18727 should prioritize immediate firmware updates from Tenda to address the root cause of the buffer overflow vulnerability. Network administrators should implement network segmentation and access controls to limit exposure of affected devices to untrusted networks while maintaining strict firewall rules to restrict external access to router management interfaces. Additional defensive measures include disabling unnecessary web server functionality, implementing intrusion detection systems to monitor for suspicious HTTP traffic patterns, and conducting regular security assessments of network infrastructure. Organizations should also consider deploying network access control mechanisms and monitoring for unusual network behavior that might indicate exploitation attempts. The vulnerability underscores the importance of secure coding practices, particularly in embedded systems where memory management errors can have severe consequences, and emphasizes the need for regular security audits of firmware components in network infrastructure devices to prevent similar issues from emerging in future releases.