CVE-2020-20746 in AC9
Summary
by MITRE • 10/01/2021
A stack-based buffer overflow in the httpd server on Tenda AC9 V15.03.06.60_EN allows remote attackers to execute arbitrary code or cause a denial of service (DoS) via a crafted POST request to /goform/SetStaticRouteCfg.
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Analysis
by VulDB Data Team • 10/04/2021
The vulnerability identified as CVE-2020-20746 represents a critical stack-based buffer overflow flaw within the httpd server component of Tenda AC9 wireless router firmware version V15.03.06.60_EN. This vulnerability resides in the web management interface's handling of HTTP POST requests directed to the specific endpoint /goform/SetStaticRouteCfg, which is designed to manage static routing configurations through the device's graphical user interface. The flaw arises from insufficient input validation and bounds checking within the server's response handling mechanism, creating an exploitable condition that can be leveraged by remote attackers without requiring authentication or physical access to the device. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which occurs when more data is written to a fixed-length buffer located on the stack than it can accommodate, leading to memory corruption that can be manipulated to execute arbitrary code or cause system instability.
The technical exploitation of this vulnerability requires a remote attacker to craft a malicious POST request that contains an oversized payload specifically designed to overflow the targeted buffer within the httpd server process. When the router processes this malformed request, the excessive data overflows into adjacent memory locations, potentially overwriting critical program execution data such as return addresses, function pointers, or other control structures. This memory corruption can result in unpredictable program behavior, including crashes that lead to denial of service conditions or more dangerously, allow attackers to inject and execute arbitrary code with the privileges of the httpd server process. The attack vector is particularly concerning because it operates over the network without requiring any authentication credentials, making it accessible to anyone who can reach the router's web management interface on port 80.
The operational impact of CVE-2020-20746 extends beyond simple service disruption to potentially enable full system compromise of affected Tenda AC9 devices. Successful exploitation could allow attackers to gain persistent access to the router's administrative functions, enabling them to modify network configurations, redirect traffic through malicious servers, or establish backdoor access points for further network infiltration. The vulnerability affects the broader ecosystem of Tenda devices running the same firmware version, creating a potential attack surface that could be leveraged for lateral movement within networks or as part of larger attack campaigns targeting home and small office networks. From an attack framework perspective, this vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol usage, specifically targeting web protocols and HTTP services, and could be categorized under T1059 for command and scripting interpreter usage when attackers attempt to execute malicious payloads through compromised router services.
Mitigation strategies for CVE-2020-20746 should prioritize immediate firmware updates from Tenda's official website, as the vendor has likely released patches addressing this specific vulnerability. Network administrators should implement strict firewall rules to restrict access to the router's web management interface from untrusted networks, particularly disabling external access to port 80 and port 443 on affected devices. Additional protective measures include monitoring network traffic for suspicious POST requests targeting the /goform/SetStaticRouteCfg endpoint and implementing intrusion detection systems that can identify and alert on malformed HTTP requests. Organizations should also consider disabling unnecessary web management services on network devices and ensuring that all firmware updates are regularly applied through secure channels to prevent exploitation of known vulnerabilities. The vulnerability demonstrates the critical importance of input validation and memory safety practices in embedded web services, aligning with industry standards that emphasize defensive programming techniques to prevent buffer overflow conditions in network-facing applications.