CVE-2022-40070 in AC21
Summary
by MITRE • 09/19/2022
Tenda AC21 V 16.03.08.15 is vulnerable to Buffer Overflow via bin/httpd, function: formSetFirewallCfg.
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Analysis
by VulDB Data Team • 10/20/2022
The vulnerability identified as CVE-2022-40070 affects the Tenda AC21 wireless router firmware version 16.03.08.15 and represents a critical buffer overflow flaw within the web server component of the device. This vulnerability resides in the bin/httpd binary and specifically manifests within the formSetFirewallCfg function, which handles firewall configuration settings submitted through the web interface. The buffer overflow occurs when the device processes user-supplied input without proper bounds checking, creating an opportunity for malicious actors to execute arbitrary code on the affected system. This type of vulnerability falls under the Common Weakness Enumeration category CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations.
The technical implementation of this vulnerability allows an attacker to exploit the buffer overflow through web-based attacks targeting the router's HTTP interface. When the formSetFirewallCfg function processes configuration data submitted via web forms, it fails to validate the length of input parameters before copying them into fixed-size buffers. This oversight enables an attacker to supply more data than the allocated buffer space, causing a stack or heap corruption that can be leveraged to execute malicious code with the privileges of the web server process. The attack vector is particularly concerning as it requires no authentication, making it accessible to remote attackers who can exploit the vulnerability from outside the network. The device's web server component runs with elevated privileges, meaning successful exploitation could provide attackers with complete control over the router's operations, including access to network traffic, configuration modifications, and potential lateral movement within the network.
The operational impact of this vulnerability extends beyond simple remote code execution, as it fundamentally compromises the security posture of any network relying on the affected Tenda AC21 devices. Once exploited, attackers can establish persistent access to the network, potentially using the router as a pivot point for further attacks against internal systems. The vulnerability's presence in the firewall configuration handling component means that attackers could disable security features, redirect traffic, or create backdoors for continued access. This aligns with ATT&CK framework technique T1071.004 for application layer protocol usage and T1566 for credential access through social engineering, as the exploitation could lead to broader network infiltration. Network administrators face significant risks as this vulnerability could go undetected for extended periods, providing attackers with uninterrupted access to the network infrastructure. The exploitation process typically involves crafting malicious input parameters that trigger the buffer overflow, potentially requiring precise payload construction to achieve reliable code execution.
Mitigation strategies for CVE-2022-40070 should prioritize immediate firmware updates from Tenda, as the vendor has likely released patches addressing this specific vulnerability. Network segmentation and firewall rules should be implemented to limit access to administrative interfaces, while disabling unnecessary web services reduces the attack surface. Regular network monitoring for unusual traffic patterns or unauthorized configuration changes can help detect exploitation attempts. Security professionals should implement network access control lists to restrict access to the affected devices and consider deploying intrusion detection systems that can identify attempts to exploit buffer overflow vulnerabilities. Additionally, maintaining detailed network documentation and regularly auditing device configurations helps ensure that any unauthorized changes are quickly identified. Organizations should also consider implementing endpoint detection and response solutions that can detect anomalous behavior indicative of exploitation attempts. The vulnerability's classification as a remote code execution flaw necessitates immediate action, as the attack surface is broad and the potential for significant network compromise is high. Regular vulnerability assessments and penetration testing should be conducted to identify similar weaknesses in other network infrastructure components, while maintaining awareness of other known vulnerabilities in networking equipment that could be exploited as part of a broader attack campaign.