CVE-2023-38823 in AC6
Summary
by MITRE • 11/20/2023
Buffer Overflow vulnerability in Tenda Ac19 v.1.0, AC18, AC9 v.1.0, AC6 v.2.0 and v.1.0 allows a remote attacker to execute arbitrary code via the formSetCfm function in bin/httpd.
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Analysis
by VulDB Data Team • 01/20/2026
This buffer overflow vulnerability exists within the Tenda wireless router firmware versions including Ac19 v.1.0, AC18, AC9 v.1.0, and AC6 v.2.0 and v.1.0, representing a critical security flaw that enables remote code execution. The vulnerability manifests through the formSetCfm function within the bin/httpd binary component, which serves as the web server interface for device management. The flaw occurs when the device processes HTTP requests containing malformed data in parameters that are directly passed to buffer operations without proper bounds checking. This type of vulnerability falls under CWE-121, which specifically addresses stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The attack vector is particularly dangerous as it enables remote exploitation without requiring authentication, making it accessible to any attacker who can reach the device's web interface. The HTTP daemon component represents a prime target for exploitation since it handles all incoming web requests and is typically accessible from external networks. This vulnerability directly maps to ATT&CK technique T1210, which describes exploitation of remote services through buffer overflow attacks.
The technical implementation of this flaw involves the formSetCfm function receiving user-supplied input through HTTP parameters that are then copied into fixed-size buffers without adequate validation. When an attacker crafts malicious input exceeding the buffer capacity, the excess data overflows into adjacent memory segments, potentially overwriting return addresses, function pointers, or other critical control data. This memory corruption can be leveraged to redirect program execution flow to attacker-controlled code, effectively enabling remote code execution on the affected devices. The specific nature of the vulnerability suggests that the firmware does not implement proper input sanitization or length validation for parameters processed by the httpd service. The exploitation process would likely involve crafting HTTP requests with oversized payloads targeting the vulnerable function, potentially utilizing techniques such as return-oriented programming or direct code injection to achieve execution control.
The operational impact of this vulnerability extends far beyond individual device compromise, as affected Tenda routers serve as network gateways for numerous households and small businesses. Once compromised, these devices can be used as entry points for broader network infiltration, enabling attackers to conduct man-in-the-middle attacks, redirect traffic, or establish persistent backdoors. The vulnerability's remote exploitability means that attackers do not require physical access to devices, significantly expanding the attack surface. Network administrators face the challenge of identifying potentially compromised devices across their networks, as the attack may not immediately produce visible symptoms. The affected firmware versions suggest this vulnerability has existed for an extended period, potentially exposing networks to long-term risk without proper patching. Organizations relying on these devices for network infrastructure may experience complete network compromise, with potential data exfiltration, service disruption, or unauthorized access to connected systems. The vulnerability also impacts the broader IoT ecosystem, as compromised routers can serve as launching points for attacks against other networked devices.
Mitigation strategies should focus on immediate firmware updates from Tenda, as the vendor has likely released patches addressing this specific buffer overflow condition. Network segmentation and firewall rules can help limit the exposure of these devices to external threats, while monitoring for unusual HTTP traffic patterns may help detect exploitation attempts. The implementation of network access control lists and disabling unnecessary services can reduce the attack surface. Organizations should also consider deploying intrusion detection systems capable of identifying malicious HTTP requests targeting the vulnerable formSetCfm function. Regular vulnerability assessments of network infrastructure should include checking for outdated firmware versions, particularly focusing on IoT devices and network equipment. The vulnerability highlights the importance of secure coding practices and proper input validation in embedded systems, emphasizing the need for comprehensive security testing of firmware components before deployment. Network administrators should also implement continuous monitoring for signs of device compromise, including unexpected network traffic patterns or unauthorized configuration changes that may indicate exploitation of this vulnerability.