CVE-2026-4489 Overview
CVE-2026-4489 is a stack-based buffer overflow vulnerability in the Tenda A18 Pro router running firmware version 02.03.02.28. The flaw resides in the form_fast_setting_wifi_set function, which handles requests sent to the /goform/fast_setting_wifi_set endpoint. Attackers can trigger the overflow by manipulating input parameters processed by this function. The issue is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). The exploit has been published, increasing the risk of opportunistic attacks against exposed devices.
Critical Impact
A remote attacker with low privileges can corrupt the router's stack memory, enabling potential code execution or denial of service against the device.
Affected Products
- Tenda A18 Pro router
- Firmware version 02.03.02.28
- /goform/fast_setting_wifi_set web management endpoint
Discovery Timeline
- 2026-03-20 - CVE-2026-4489 published to NVD
- 2026-04-22 - Last updated in NVD database
Technical Details for CVE-2026-4489
Vulnerability Analysis
The vulnerability exists in the form_fast_setting_wifi_set function, which processes Wi-Fi quick-setup requests submitted to the /goform/fast_setting_wifi_set URI. The function copies user-supplied data into a fixed-size stack buffer without enforcing length validation. When an attacker submits an oversized parameter, the copy operation overruns the buffer and overwrites adjacent stack memory, including saved return addresses. This is classified under [CWE-119] as an improper restriction of memory buffer operations. The condition is reachable over the network and requires only low privileges to exploit. Publicly available exploit code lowers the technical barrier for adversaries targeting exposed devices.
Root Cause
The root cause is the absence of bounds checking inside form_fast_setting_wifi_set before writing attacker-controlled HTTP parameter values into a stack-allocated buffer. The firmware trusts the length of values supplied through the web management form. Without explicit size validation or use of length-bounded copy primitives, oversized inputs corrupt the call stack and adjacent local variables.
Attack Vector
The attack vector is network-based. An authenticated attacker with access to the router's web management interface sends a crafted HTTP POST request to /goform/fast_setting_wifi_set containing an overlong parameter value. Successful exploitation can result in stack corruption, device crash, or arbitrary code execution within the context of the embedded HTTP service. Routers with management interfaces exposed beyond the LAN face the highest risk.
For technical details, see the GitHub Issue Tracking and VulDB #352015.
Detection Methods for CVE-2026-4489
Indicators of Compromise
- Unexpected HTTP POST requests to /goform/fast_setting_wifi_set containing abnormally long parameter values.
- Router reboots, watchdog resets, or HTTP daemon crashes following requests to the fast-setup endpoint.
- Authentication events to the router web UI from unfamiliar source addresses preceding the suspicious requests.
Detection Strategies
- Inspect router and gateway logs for repeated requests targeting /goform/fast_setting_wifi_set with payloads exceeding expected parameter lengths.
- Deploy network intrusion detection signatures that flag oversized form fields directed at Tenda /goform/ endpoints.
- Correlate failed administrative logins with subsequent requests to Wi-Fi setup endpoints to surface exploitation attempts.
Monitoring Recommendations
- Forward router syslog data and HTTP access logs to a centralized analytics platform for retention and search.
- Alert on HTTP request body sizes that exceed established baselines for the affected endpoint.
- Track outbound connections originating from the router, which may indicate post-exploitation activity following stack corruption.
How to Mitigate CVE-2026-4489
Immediate Actions Required
- Restrict access to the router's web management interface to trusted internal hosts only and disable WAN-side administration.
- Change default and weak administrative credentials to reduce the chance of an attacker reaching the authenticated endpoint.
- Audit network exposure of Tenda A18 Pro devices and remove unnecessary remote management exposure.
Patch Information
At the time of publication, no vendor-supplied patch is referenced in the available CVE data. Refer to the Tenda Website Overview for firmware release announcements and contact vendor support for guidance on remediation timelines.
Workarounds
- Place the affected router behind an upstream firewall and block external access to /goform/fast_setting_wifi_set.
- Segment IoT and management networks so that only administrative workstations can reach the router web UI.
- Replace the device with supported hardware if a fixed firmware version is not made available by the vendor.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
