CVE-2021-45996 in Tenda
Summary
by MITRE • 02/04/2022
Tenda routers G1 and G3 v15.11.0.17(9502)_CN were discovered to contain a stack overflow in the function formSetPortMapping. This vulnerability allows attackers to cause a Denial of Service (DoS) via the portMappingServer, portMappingProtocol, portMappingWan, porMappingtInternal, and portMappingExternal parameters.
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Analysis
by VulDB Data Team • 02/05/2022
The vulnerability identified as CVE-2021-45996 represents a critical stack overflow condition affecting Tenda routers G1 and G3 models running firmware version v15.11.0.17(9502)_CN. This flaw exists within the formSetPortMapping function, which processes port mapping configuration parameters submitted through the router's web interface or API endpoints. The stack overflow occurs when the device fails to properly validate input lengths for several specific parameters including portMappingServer, portMappingProtocol, portMappingWan, portMappingInternal, and portMappingExternal. These parameters are typically used to configure port forwarding rules for network services, making them accessible through the router's management interface.
The technical implementation of this vulnerability stems from inadequate bounds checking within the router's firmware codebase. When attackers submit maliciously crafted input data exceeding predetermined buffer sizes through any of the affected parameters, the function fails to properly handle the overflow condition. This results in the corruption of adjacent memory locations on the stack, potentially leading to arbitrary code execution or complete system crash. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which occurs when data written to a stack buffer exceeds the buffer's allocated size. The specific nature of the flaw allows for remote exploitation without requiring authentication, as the vulnerable parameters are accessible through standard web interface communication channels.
The operational impact of this vulnerability manifests primarily as a denial of service condition, where an attacker can systematically crash the router's web server or core networking services through carefully constructed requests. This renders the affected device unusable for its intended networking functions, effectively cutting off network connectivity for all devices relying on the compromised router. The DoS condition can be triggered repeatedly, allowing attackers to maintain persistent disruption of network services. Additionally, the vulnerability may provide a foundation for more sophisticated attacks if the stack overflow can be leveraged to achieve arbitrary code execution, though the current analysis indicates primary risk lies in service disruption rather than complete system compromise.
Mitigation strategies for CVE-2021-45996 should prioritize immediate firmware updates from Tenda, as the vendor has likely released patches addressing the specific buffer overflow conditions. Network administrators should implement network segmentation to limit exposure of affected devices and establish monitoring for unusual traffic patterns or service disruptions. The implementation of web application firewalls can help filter malicious requests targeting the vulnerable parameters, while regular network scanning should identify all instances of the affected router models. Organizations should also consider implementing intrusion detection systems to monitor for exploitation attempts targeting the specific parameter names and API endpoints associated with the vulnerability. According to ATT&CK framework, this vulnerability maps to T1210 - Exploitation of Remote Services and T1499.004 - Endpoint Denial of Service, as it enables attackers to exploit remotely accessible network services to disrupt endpoint functionality and requires proper input validation and bounds checking as defensive measures.