CVE-2022-25440 in AC9
Summary
by MITRE • 03/19/2022
Tenda AC9 v15.03.2.21 was discovered to contain a stack overflow via the ntpserver parameter in the SetSysTimeCfg function.
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Analysis
by VulDB Data Team • 03/23/2022
The vulnerability identified as CVE-2022-25440 represents a critical stack overflow flaw within the Tenda AC9 wireless router firmware version 15.03.2.21. This issue manifests through the improper handling of the ntpserver parameter within the SetSysTimeCfg function, creating a potential pathway for remote code execution and system compromise. The vulnerability resides in the router's web interface configuration handling mechanism, where user-supplied input is processed without adequate bounds checking or validation.
The technical implementation of this flaw stems from inadequate input sanitization within the firmware's time synchronization configuration component. When the ntpserver parameter is submitted through the web interface to the SetSysTimeCfg function, the system fails to properly validate the length or content of the input string before copying it to a fixed-size buffer on the stack. This classic buffer overflow condition allows an attacker to overwrite adjacent stack memory locations, potentially including return addresses and function pointers, thereby enabling arbitrary code execution. The vulnerability aligns with CWE-121, which specifically addresses stack-based buffer overflow conditions where insufficient bounds checking permits buffer overflows to occur.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it provides attackers with the capability to execute malicious code with the privileges of the affected service. An unauthenticated remote attacker could exploit this vulnerability by crafting a specially formatted HTTP request containing an oversized ntpserver parameter value. Successful exploitation could result in complete system compromise, allowing attackers to gain persistent access to the network, modify router configuration, redirect traffic, or establish backdoor access points. The attack surface is particularly concerning given that routers serve as primary network gateways and often have direct access to internal network resources.
This vulnerability directly maps to several ATT&CK techniques including T1059.007 for command and script interpreter, T1068 for exploit for privilege escalation, and T1566 for phishing with malicious attachments or links. The attack chain typically involves initial reconnaissance to identify vulnerable firmware versions, followed by exploitation of the stack overflow to gain remote code execution capabilities. Network defenders should note that this vulnerability affects not only the specific Tenda AC9 model but potentially other router models using similar firmware components, making it a widespread concern for network security professionals.
Mitigation strategies should include immediate firmware updates from Tenda to address the buffer overflow condition, implementation of network segmentation to limit exposure, and deployment of intrusion detection systems capable of identifying suspicious HTTP requests targeting the affected parameter. Additionally, network administrators should consider disabling unnecessary web management interfaces and implementing strict access controls. The vulnerability highlights the importance of input validation and proper bounds checking in embedded firmware development, as recommended by industry best practices and security frameworks that emphasize defensive programming techniques to prevent such memory corruption vulnerabilities from being exploited in real-world scenarios.