CVE-2018-18731 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 'deviceMac' parameter 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
The vulnerability identified as CVE-2018-18731 represents a critical buffer overflow flaw within the web server component of several Tenda wireless router models including AC7, AC9, AC10, AC15, and AC18. This issue manifests specifically when the httpd web server processes POST requests containing the 'deviceMac' parameter, creating a dangerous condition that can be exploited by remote attackers to gain unauthorized control over affected devices. The vulnerability stems from improper input validation and handling within the router's firmware, where user-supplied data is directly incorporated into stack-based string operations without adequate bounds checking.
The technical implementation of this flaw involves the direct usage of the 'deviceMac' parameter within a sprintf function call that writes data to a local stack variable. This programming error creates a classic stack-based buffer overflow condition where the excessive input data overflows the allocated buffer space and subsequently overwrites the function's return address stored on the stack. According to CWE-121, this vulnerability maps directly to stack-based buffer overflow conditions that occur when insufficient bounds checking allows data to overwrite adjacent memory locations. The compromised return address creates an opportunity for attackers to redirect program execution flow and potentially execute arbitrary code with the privileges of the httpd process.
The operational impact of this vulnerability extends beyond simple remote code execution, as it enables attackers to completely compromise the affected router devices. Once exploited, the attacker gains access to the router's administrative interface and can modify network configurations, intercept traffic, install malicious firmware, or use the device as a pivot point for further attacks within the local network. The vulnerability affects multiple router models from the same manufacturer, indicating a widespread firmware issue that could impact thousands of devices deployed in residential and small business environments. This represents a significant concern for network security as compromised routers can serve as persistent backdoors for ongoing surveillance or as launching points for larger-scale attacks.
Mitigation strategies for this vulnerability should prioritize immediate firmware updates from Tenda, as the manufacturer would have likely released patches addressing this specific buffer overflow condition. Network administrators should also implement network segmentation and monitoring to detect suspicious traffic patterns that might indicate exploitation attempts. The vulnerability's characteristics align with ATT&CK technique T1059.007 for command and scripting interpreter, as exploitation would likely involve injecting malicious commands through the vulnerable web interface. Additionally, implementing proper input validation and using safe string handling functions such as snprintf instead of sprintf would prevent similar issues in future firmware development. Organizations should also consider network access control lists to restrict access to router administrative interfaces and implement intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability.