CVE-2018-18728 in AC9
Summary
by MITRE
An issue was discovered on Tenda AC9 V15.03.05.19(6318)_CN, AC15 V15.03.05.19_CN, and AC18 V15.03.05.19(6318)_CN devices. They allow remote code execution via shell metacharacters in the usbName field to the __fastcall function with a POST request.
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Analysis
by VulDB Data Team • 04/07/2020
This vulnerability exists in Tenda wireless routers running specific firmware versions including AC9 V15.03.05.19(6318)_CN, AC15 V15.03.05.19_CN, and AC18 V15.03.05.19(6318)_CN. The flaw resides in the handling of the usbName parameter within a POST request to a function named __fastcall, which processes USB device naming configurations. The vulnerability stems from insufficient input validation and sanitization of user-supplied data, allowing malicious actors to inject shell metacharacters directly into the usbName field. This represents a classic command injection vulnerability where untrusted input flows directly into system commands without proper sanitization or escaping mechanisms.
The technical implementation of this vulnerability enables remote code execution through a carefully crafted POST request that targets the usbName parameter. When the firmware processes this parameter, it fails to properly escape or validate shell metacharacters such as semicolons, ampersands, or backticks that could be used to chain commands. The __fastcall function serves as the entry point where this unsafe processing occurs, making it a critical attack surface for privilege escalation. This vulnerability aligns with CWE-77 which specifically addresses command injection flaws in software systems. The attack vector requires no authentication and can be executed remotely, making it particularly dangerous for network-connected devices.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass complete system compromise and potential lateral movement within networks. An attacker who successfully exploits this vulnerability gains full control over the affected router, potentially enabling them to modify network configurations, redirect traffic, establish backdoors, or use the device as a pivot point for attacking other systems within the local network. This aligns with ATT&CK technique T1059 which covers command and scripting interpreter usage, and T1021 which addresses remote services exploitation. The affected devices could serve as persistent command and control nodes for broader network attacks, especially in environments where router security is not adequately considered.
Mitigation strategies for this vulnerability should include immediate firmware updates from Tenda to address the command injection flaw, network segmentation to limit access to these devices, and implementation of intrusion detection systems to monitor for suspicious POST requests targeting the affected parameter. Network administrators should also consider disabling unnecessary USB functionality if not required, as this reduces the attack surface. The vulnerability demonstrates the critical importance of input validation and proper sanitization of user-supplied data in network appliances, particularly those handling system-level operations. Organizations should implement comprehensive vulnerability management programs that include regular firmware updates and security assessments of network infrastructure devices to prevent exploitation of similar command injection vulnerabilities.