CVE-2023-40891 in AC8
Summary
by MITRE • 08/24/2023
Tenda AC8 v4 US_AC8V4.0si_V16.03.34.06_cn was discovered to contain a stack overflow via parameter firewallEn at /goform/SetFirewallCfg.
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Analysis
by VulDB Data Team • 01/30/2026
The vulnerability identified as CVE-2023-40891 affects the Tenda AC8 v4 US_AC8V4.0si_V16.03.34.06_cn router firmware, representing a critical stack overflow condition that can be exploited through the firewallEn parameter within the /goform/SetFirewallCfg API endpoint. This issue resides in the web interface handling of firewall configuration parameters, where inadequate input validation allows maliciously crafted data to overwrite stack memory beyond allocated boundaries. The vulnerability manifests when the device processes the firewallEn parameter, which is used to enable or disable firewall functionality, creating an opportunity for remote code execution or system compromise through carefully constructed input data.
The technical flaw stems from improper bounds checking and memory management within the firmware's web application layer, specifically in how it handles the firewallEn parameter during form processing. When an attacker submits a malformed value for firewallEn, the application fails to validate the input length or content, allowing a buffer overflow condition to occur. This vulnerability is classified as CWE-121 Stack-based Buffer Overflow, which directly maps to the ATT&CK technique T1203 Exploitation for Client Execution through web interface manipulation. The stack overflow occurs because the application uses unsafe string handling functions that do not perform adequate bounds checking, enabling an attacker to overwrite adjacent memory locations including return addresses and control flow information.
The operational impact of this vulnerability extends beyond simple denial of service, as it potentially enables complete system compromise through remote code execution. An attacker who successfully exploits this vulnerability can gain arbitrary code execution privileges on the affected router, allowing for persistent access, network monitoring, data exfiltration, or use as a pivot point for attacking other devices within the local network. The attack surface is particularly concerning given that the vulnerability exists in a web-based management interface that is often accessible from external networks, especially when routers are configured with remote administration enabled. The affected device's firmware version indicates it likely lacks proper input sanitization and memory protection mechanisms, making it susceptible to exploitation without requiring physical access or advanced attack capabilities.
Mitigation strategies for CVE-2023-40891 should prioritize immediate firmware updates from Tenda, as the vendor has likely released patches addressing the stack overflow condition. Network administrators should also implement strict firewall rules to restrict access to the router's web management interface, particularly from external networks, and disable remote administration features when not required. Additional defensive measures include monitoring for unusual traffic patterns or attempts to access the vulnerable /goform/SetFirewallCfg endpoint, implementing network segmentation to limit lateral movement, and regularly auditing device configurations for unnecessary services or open ports. The vulnerability demonstrates the importance of input validation and secure coding practices, particularly when handling user-supplied data in web applications, aligning with ATT&CK's emphasis on preventing exploitation through proper application security controls and defensive programming techniques.