CVE-2026-2139 is a buffer overflow vulnerability identified in the Tenda TX9 router firmware up to version 22.03.02.10_multi. The vulnerability resides in the function sub_432580 within the /goform/fast_setting_wifi_set endpoint, which processes the ssid parameter. Improper validation or sanitization of this input allows an attacker to overflow a buffer, potentially overwriting adjacent memory. This can lead to arbitrary code execution, denial of service, or device takeover. The vulnerability is remotely exploitable without requiring authentication or user interaction, making it particularly dangerous. The CVSS 4.0 base score is 8.7 (high), reflecting the ease of exploitation (network vector, low attack complexity), no privileges required, and high impact on confidentiality, integrity, and availability. Although no known exploits are currently active in the wild, public disclosure of exploit code increases the likelihood of imminent attacks. The vulnerability affects a widely deployed consumer and small business router model, which may be used in various European organizations, especially in small offices or home office environments. The lack of available patches at the time of disclosure necessitates immediate mitigation through network segmentation, access control, and monitoring for suspicious activity targeting the vulnerable endpoint.

For European organizations, exploitation of CVE-2026-2139 could result in complete compromise of affected Tenda TX9 routers, leading to unauthorized network access, interception or manipulation of network traffic, and potential pivoting to internal networks. This threatens confidentiality by exposing sensitive data, integrity by allowing alteration of network configurations or injected malicious payloads, and availability by causing device crashes or persistent denial of service. Small and medium enterprises relying on these routers for critical connectivity are particularly vulnerable. The attack can be launched remotely without authentication, increasing the attack surface. Disruption of network infrastructure could impact business operations, especially in sectors with high reliance on stable internet connectivity such as finance, healthcare, and manufacturing. Additionally, compromised routers could be leveraged as part of botnets or for launching further attacks, amplifying the threat landscape in Europe.

1. Immediately restrict external network access to the router’s management interface (/goform/fast_setting_wifi_set endpoint) using firewall rules or network segmentation to prevent remote exploitation. 2. Monitor network traffic for unusual requests targeting the vulnerable endpoint or abnormal router behavior indicative of exploitation attempts. 3. Apply vendor-provided firmware updates or patches as soon as they become available to remediate the buffer overflow. 4. If patches are not yet available, consider temporarily replacing vulnerable devices or disabling remote management features. 5. Implement strong network access controls and authentication mechanisms to limit administrative access to trusted personnel and networks. 6. Conduct regular security audits of network devices to identify outdated firmware and vulnerabilities. 7. Educate IT staff about this vulnerability and encourage vigilance for indicators of compromise related to router exploitation. 8. Employ intrusion detection/prevention systems capable of detecting buffer overflow attack patterns targeting router management interfaces.