CVE-2026-24111 is a critical security vulnerability identified in the Tenda W20E router firmware version V4.0br_V15.11.0.6. The vulnerability stems from improper input validation in the addAuthUser function, where the 'userInfo' parameter is processed using the C standard library function sscanf without enforcing size constraints. This lack of boundary checking leads to a classic buffer overflow condition (CWE-120), allowing an attacker to overwrite adjacent memory. Exploitation requires no authentication or user interaction and can be performed remotely over the network, making it highly accessible to attackers. Successful exploitation could enable arbitrary code execution, complete system takeover, or denial of service by corrupting memory structures. The vulnerability was reserved on January 21, 2026, and published on March 2, 2026, with a CVSS v3.1 base score of 9.8, reflecting its critical severity. No patches or known exploits have been reported yet, but the risk remains significant due to the ease of exploitation and potential impact. The vulnerability affects a widely deployed consumer and small business router model, which is often used as a gateway device, increasing the potential attack surface and impact scope.

The impact of CVE-2026-24111 is severe for organizations using the affected Tenda W20E routers. Exploitation can lead to full compromise of the device, allowing attackers to execute arbitrary code with system privileges. This can result in unauthorized access to internal networks, interception or manipulation of network traffic, disruption of network availability, and potential pivoting to other internal systems. The confidentiality, integrity, and availability of network communications and connected devices are all at risk. Given that routers serve as critical infrastructure for network connectivity, a successful attack could cause widespread operational disruption and data breaches. The vulnerability's remote, unauthenticated exploit vector increases the likelihood of attacks, including automated scanning and exploitation by threat actors. Organizations relying on these devices without mitigation or patching face significant security exposure.

To mitigate CVE-2026-24111, organizations should immediately verify if their network infrastructure includes Tenda W20E routers running firmware version V4.0br_V15.11.0.6. Since no official patches are currently available, interim mitigations include: 1) Restricting remote management access to the router by disabling WAN-side administration interfaces or limiting access via firewall rules to trusted IP addresses only. 2) Segmenting the network to isolate the router management interface from untrusted networks. 3) Monitoring network traffic for unusual activity or exploitation attempts targeting the addAuthUser function or related endpoints. 4) Engaging with Tenda support channels to obtain firmware updates or advisories. 5) Planning for device replacement if no timely patch is provided, especially in high-risk environments. 6) Employing network intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics to detect exploitation attempts. These steps help reduce exposure until a secure firmware update is released.