CVE-2026-24112 Overview
CVE-2026-24112 is a stack buffer overflow vulnerability in the Tenda W20E router running firmware version V4.0br_V15.11.0.6. The flaw resides in the addWewifiWhiteUser function, which processes the userInfo parameter using sscanf without enforcing destination buffer size limits. A remote attacker can craft an oversized userInfo value to corrupt adjacent stack memory. Successful exploitation can result in denial of service or arbitrary code execution on the device. The vulnerability is categorized under [CWE-120] (Classic Buffer Overflow) and is reachable over the network without authentication or user interaction.
Critical Impact
Unauthenticated remote attackers can trigger a stack buffer overflow in the addWewifiWhiteUser function, potentially leading to arbitrary code execution on affected Tenda W20E routers.
Affected Products
- Tenda W20E hardware version 4.0
- Tenda W20E firmware V15.11.0.6
- Tenda W20E firmware identifier V4.0br_V15.11.0.6
Discovery Timeline
- 2026-03-02 - CVE-2026-24112 published to the National Vulnerability Database
- 2026-03-03 - Last updated in NVD database
Technical Details for CVE-2026-24112
Vulnerability Analysis
The Tenda W20E web management interface exposes a handler that invokes the addWewifiWhiteUser function when processing Wi-Fi white-list user additions. The function accepts attacker-controlled userInfo data and parses it with sscanf using format specifiers that do not constrain field width. Because the destination buffer on the stack has a fixed size, parsing oversized input writes past the buffer boundary. This overwrites adjacent stack data, including saved registers and the return address. An attacker with network reach to the router's management service can deliver the malicious payload through a crafted HTTP request. Because the router runs the affected service with elevated privileges, code execution grants full control over the device.
Root Cause
The root cause is missing input length validation prior to the sscanf call inside addWewifiWhiteUser. The %s format specifier in sscanf reads until whitespace or end-of-string with no upper bound. Developers should have either bounded the conversion with a width specifier such as %Ns or pre-validated the input length against the destination buffer size.
Attack Vector
Exploitation requires only network access to the router's HTTP management interface. The attacker submits a request containing an oversized userInfo parameter to the vulnerable endpoint. No credentials or user interaction are required. If management is exposed to the WAN, the device is reachable directly from the internet. On LAN deployments, an attacker on the local network or any compromised internal host can reach the endpoint.
No verified public proof-of-concept code is available. Technical analysis is published in the GitHub CVE-2026-24112 Report.
Detection Methods for CVE-2026-24112
Indicators of Compromise
- HTTP requests to the router management interface containing abnormally long userInfo parameter values, particularly to endpoints invoking addWewifiWhiteUser.
- Unexpected reboots, watchdog resets, or crash logs from the Tenda W20E web management daemon.
- New or modified Wi-Fi white-list entries that do not correspond to administrator activity.
- Outbound connections from the router to unknown hosts following management interface activity.
Detection Strategies
- Inspect HTTP/HTTPS traffic destined for the router management port for parameter values exceeding expected lengths.
- Deploy network intrusion detection signatures that flag requests with oversized userInfo fields targeting Tenda W20E URI patterns.
- Correlate router crash events with preceding inbound HTTP requests in upstream firewall or switch logs.
Monitoring Recommendations
- Forward router syslog data to a centralized logging or SIEM platform and alert on repeated daemon restarts.
- Monitor management interface exposure by scanning the WAN side of the device to confirm administrative ports are not internet-reachable.
- Track configuration changes to the Wi-Fi white list and alert on additions outside of change windows.
How to Mitigate CVE-2026-24112
Immediate Actions Required
- Restrict access to the router web management interface to trusted administrative hosts only and disable WAN-side management.
- Place vulnerable Tenda W20E devices behind a network segment that filters inbound HTTP traffic to the management port.
- Audit Wi-Fi white-list configurations and remove unauthorized entries.
- Consult the Tenda Security Information page for vendor updates and firmware availability.
Patch Information
No fixed firmware version has been published in the NVD reference data at the time of disclosure. Administrators should monitor Tenda's official advisory channel for an updated firmware release that addresses the sscanf length validation in addWewifiWhiteUser. Where a patched firmware is unavailable, treat affected devices as untrusted and apply compensating network controls.
Workarounds
- Disable remote management on the WAN interface through the router administration console.
- Apply access control lists on upstream network equipment to permit management traffic only from designated administrative subnets.
- Replace end-of-life or unsupported Tenda W20E units with actively maintained hardware if no firmware fix becomes available.
- Change administrator credentials and rotate Wi-Fi keys after isolating the device, in case prior exploitation has occurred.
# Example upstream firewall rule to block external access to router management
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -i <wan_iface> -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -i <wan_iface> -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
