CVE-2026-104611 in AC9
Summary
by MITRE • 10/02/2026
A vulnerability was detected in Tenda AC9 15.03.02.13. Affected is an unknown function of the file /goform/fast_setting_internet_set of the component POST Request Handler. Performing a manipulation of the argument netWanType results in stack-based buffer overflow. The attack is possible to be carried out remotely. The exploit is now public and may be used.
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Analysis
by VulDB Data Team • 10/02/2026
The Tenda AC9 router, specifically running firmware version 15.03.02.13, contains a critical security flaw within its web-based management interface that allows for remote code execution through stack-based buffer overflow exploitation. This vulnerability resides in the POST request handler component, which processes configuration updates submitted by users or attackers via HTTP requests. The specific point of failure is located in the file /goform/fast_setting_internet_set, a script responsible for handling fast setup configurations related to internet connectivity settings. When an attacker manipulates the netWanType argument during a POST request, they can supply input data that exceeds the allocated buffer size on the stack. This overflow overwrites adjacent memory locations, including critical control data such as return addresses and saved frame pointers, thereby allowing the attacker to redirect program execution flow.
From a technical perspective, this flaw is classified under CWE-121, which denotes a stack-based buffer overflow condition. The vulnerability arises because the application fails to properly validate or sanitize the length of the netWanType parameter before copying it into a fixed-size buffer on the call stack. In embedded systems like routers, such memory corruption issues are particularly dangerous as they can lead not only to denial-of-service conditions through crashes but also to arbitrary code execution if an attacker carefully crafts shellcode and overwrites function pointers or return addresses with malicious payloads. The presence of this vulnerability in a network-facing service means that it is accessible from untrusted networks, significantly increasing the attack surface for potential intrusions into home or small business networks.
The operational impact of exploiting this vulnerability is severe, as it grants an attacker remote access to the router's operating system without requiring authentication if the web interface is exposed to the internet or if a victim is tricked into making a request while connected to the same network in some configurations. Successful exploitation can lead to full compromise of the device, allowing attackers to intercept traffic, redirect DNS queries for phishing campaigns, install persistent malware such as botnet agents like Mirai variants, or use the compromised router as a pivot point to attack other devices on the local network. The fact that public exploits are available further exacerbates this risk, enabling automated scanning tools and opportunistic attackers to easily identify and compromise vulnerable instances across the internet with minimal technical effort.
This vulnerability aligns with MITRE ATT&CK techniques related to initial access and execution via web applications. Specifically, it falls under T1190, Exploit Public-Facing Application, where adversaries leverage vulnerabilities in services exposed to external networks to gain a foothold. Additionally, the mechanism of stack-based buffer overflow is often associated with privilege escalation or code injection tactics depending on how the exploit payload is constructed and executed within the router's limited environment. The availability of public exploits means that this vulnerability has moved beyond theoretical risk into active exploitation territory, making it imperative for administrators to take immediate action.
Mitigation strategies should focus primarily on updating the firmware to a patched version released by Tenda that addresses the buffer validation logic in the /goform/fast_setting_internet_set handler. If an update is not immediately available or applicable due to hardware limitations, network-level controls become essential. Administrators should ensure that the router's web management interface is not exposed directly to the internet via port forwarding rules on upstream firewalls. Instead, access should be restricted to local area networks only. Implementing strict input validation at the firewall level for HTTP POST requests targeting this specific endpoint can also provide a layer of defense against malformed packets attempting to trigger the overflow. Regular monitoring of network traffic for anomalous patterns associated with buffer overflow attempts and keeping all connected devices updated further reduces the overall risk profile in environments utilizing these routers.