CVE-2017-16923 in Tenda
Summary
by MITRE
Command Injection vulnerability in app_data_center on Shenzhen Tenda Ac9 US_AC9V1.0BR_V15.03.05.14_multi_TD01, Ac9 ac9_kf_V15.03.05.19(6318_)_cn, Ac15 US_AC15V1.0BR_V15.03.05.18_multi_TD01, Ac15 US_AC15V1.0BR_V15.03.05.19_multi_TD01, Ac18 US_AC18V1.0BR_V15.03.05.05_multi_TD01, and Ac18 ac18_kf_V15.03.05.19(6318_)_cn devices allows remote unauthenticated attackers to execute arbitrary OS commands via a crafted cgi-bin/luci/usbeject?dev_name= GET request from the LAN. This occurs because the "sub_A6E8 usbeject_process_entry" function executes a system function with untrusted input.
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Analysis
by VulDB Data Team • 12/09/2019
The CVE-2017-16923 vulnerability represents a critical command injection flaw within the Shenzhen Tenda wireless router firmware ecosystem, specifically affecting multiple AC series devices including AC9, AC15, and AC18 models. This vulnerability exists in the app_data_center component of the firmware and manifests through the cgi-bin/luci/usbeject?dev_name= endpoint, which processes GET requests from local network clients without proper input validation. The flaw allows remote unauthenticated attackers on the local network to execute arbitrary operating system commands by crafting malicious requests that exploit the insecure handling of user-supplied parameters. The vulnerability stems from the "sub_A6E8 usbeject_process_entry" function which directly invokes system commands using untrusted input, creating a direct path for command injection attacks.
This vulnerability aligns with CWE-77, which describes improper neutralization of special elements used in operating system commands, and represents a classic example of command injection in embedded systems. The attack vector specifically targets the USB eject functionality within the web interface's user management system, where the device fails to properly sanitize the dev_name parameter before passing it to system execution functions. The affected firmware versions include US_AC9V1.0BR_V15.03.05.14_multi_TD01, Ac9 ac9_kf_V15.03.05.19(6318_)cn, US_AC15V1.0BR_V15.03.05.18_multi_TD01, US_AC15V1.0BR_V15.03.05.19_multi_TD01, US_AC18V1.0BR_V15.03.05.05_multi_TD01, and ac18_kf_V15.03.05.19(6318)_cn, indicating a widespread issue across multiple device variants. The vulnerability enables attackers to execute arbitrary commands with the privileges of the web server process, potentially allowing full system compromise and unauthorized access to network resources.
From an operational perspective, this vulnerability poses significant risks to network security as it allows attackers to execute commands remotely from within the local network without requiring authentication credentials. The impact includes potential data exfiltration, system compromise, and unauthorized network access, with the attack surface extending to all devices running the vulnerable firmware versions. The vulnerability maps to several ATT&CK techniques including T1059.001 for command and script interpreters, T1068 for exploit for privilege escalation, and T1566 for spearphishing with a malicious attachment, though in this case the attack is initiated through a web interface rather than email. The flaw essentially transforms the device's USB management interface into a command execution backdoor, potentially allowing attackers to modify system files, install malware, or establish persistent access to the network infrastructure.
The recommended mitigation strategies include immediate firmware updates from Tenda to address the command injection vulnerability, implementing network segmentation to isolate affected devices, and deploying intrusion detection systems to monitor for suspicious web requests targeting the vulnerable endpoint. Network administrators should also consider disabling unnecessary web interfaces and USB functionality when not required, and regularly audit device configurations to ensure no unauthorized modifications have occurred. Additionally, implementing proper input validation and output encoding practices in the web application code would prevent similar vulnerabilities from occurring in future firmware releases. Organizations should also conduct regular vulnerability assessments of their embedded network infrastructure and maintain up-to-date patch management procedures to protect against similar command injection attacks in other network devices. The vulnerability serves as a reminder of the critical importance of secure coding practices in embedded systems and the need for comprehensive security testing of network device firmware before deployment.