CVE-2026-25857 is an OS command injection vulnerability classified under CWE-78 affecting the WAN diagnostic functionality (formSetWanDiag) of Shenzhen Tenda Technology's G300-F router firmware version 16.01.14.2 and prior. The vulnerability stems from improper neutralization of special elements in the construction of a shell command that invokes curl. Specifically, the firmware incorporates attacker-controlled input directly into the command line without adequate sanitization or escaping, enabling an attacker with access to the router's management interface to inject arbitrary shell syntax. This injection allows execution of arbitrary commands with the privileges of the management process, which typically has elevated rights on the device. The vulnerability is remotely exploitable over the network without requiring user interaction, but it does require the attacker to have high privileges on the management interface, which may be protected by authentication but could be exposed due to misconfiguration or weak credentials. The CVSS v4.0 score is 8.6 (high severity), reflecting the network attack vector, low attack complexity, no required privileges beyond management interface access, and high impact on confidentiality, integrity, and availability. No patches or known exploits are currently available, increasing the urgency for defensive measures. The vulnerability could lead to full device compromise, enabling attackers to manipulate network traffic, pivot into internal networks, or disrupt services.

For European organizations, this vulnerability poses a significant risk, particularly for those using Tenda G300-F routers in their network infrastructure. Successful exploitation could lead to complete device compromise, allowing attackers to intercept or redirect network traffic, deploy malware, or establish persistent footholds within corporate or critical infrastructure networks. This could result in data breaches, service disruptions, and loss of network integrity. Organizations in sectors such as telecommunications, government, finance, and critical infrastructure are especially at risk due to the potential for attackers to leverage compromised routers as entry points for broader network attacks. The lack of available patches means that vulnerable devices remain exposed, increasing the window of opportunity for attackers. Additionally, if management interfaces are exposed to the internet or poorly segmented, the likelihood of exploitation increases. The impact extends beyond individual organizations to potentially affect national cybersecurity postures if widely deployed devices are compromised.

1. Immediately restrict access to the router's management interface by limiting it to trusted internal networks and disabling remote management if not strictly necessary. 2. Implement strong authentication mechanisms for the management interface, including complex passwords and, if supported, multi-factor authentication. 3. Segment networks to isolate management interfaces from general user and internet-facing networks, reducing exposure. 4. Monitor network traffic for unusual or suspicious WAN diagnostic requests or command injection patterns targeting the router. 5. Regularly audit router configurations to ensure no unintended exposure of management interfaces. 6. Engage with Shenzhen Tenda Technology for firmware updates or patches addressing this vulnerability and plan prompt deployment once available. 7. Consider replacing vulnerable devices with models from vendors with robust security track records if patches are delayed. 8. Educate network administrators about the risks of exposing management interfaces and the importance of secure configurations. 9. Employ network intrusion detection systems (NIDS) tuned to detect exploitation attempts targeting this vulnerability. 10. Maintain an incident response plan to quickly isolate and remediate compromised devices.