CVE-2025-57639 is an OS command injection vulnerability identified in the Tenda AC9 router firmware version 1.0. The vulnerability exists in the formSetSambaConf function within the httpd service, specifically through the usb.samba.guest.user parameter. This parameter is used to configure Samba guest user settings, and due to insufficient input validation or sanitization, it allows an attacker to inject arbitrary OS commands. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). Successful exploitation could lead to limited confidentiality and integrity impacts, such as unauthorized access to sensitive information or modification of configuration files. However, availability impact is not evident. The CVSS score of 6.5 (medium severity) reflects these factors. No known exploits are currently reported in the wild, and no patches have been published yet. The underlying weakness corresponds to CWE-78 (Improper Neutralization of Special Elements used in an OS Command). Given the nature of the vulnerability, attackers could leverage it to execute arbitrary commands on the router, potentially gaining control over the device or pivoting into the internal network. The lack of authentication requirement makes this a significant risk for exposed devices, especially those with Samba services enabled for USB sharing.

For European organizations, this vulnerability poses a moderate risk primarily to network infrastructure relying on Tenda AC9 routers, especially in small to medium enterprises or home office environments where such consumer-grade devices are common. Exploitation could lead to unauthorized disclosure of network configuration or user data accessible via Samba shares, alteration of router settings, or use of the compromised router as a foothold for further attacks within the corporate network. While the impact on availability is low, the integrity and confidentiality risks could facilitate lateral movement or data exfiltration. Organizations with remote or unmanaged deployments of Tenda AC9 devices are particularly vulnerable. Given the medium severity and lack of authentication, attackers could scan for exposed devices and exploit them remotely, increasing the threat surface. The absence of known exploits currently reduces immediate risk but does not eliminate the potential for future attacks once exploit code becomes available.

Organizations should immediately identify any Tenda AC9 routers in their environment and verify if the vulnerable Samba guest user configuration is enabled. Until an official patch is released, it is recommended to disable Samba USB sharing features or restrict access to the router's management interface to trusted internal networks only. Network segmentation should be enforced to isolate vulnerable devices from critical infrastructure. Monitoring network traffic for unusual command execution patterns or unauthorized Samba access attempts can help detect exploitation attempts. Applying strict input validation and sanitization on user-configurable parameters is essential for the vendor's patch development. Additionally, organizations should consider replacing consumer-grade routers with enterprise-grade devices that receive timely security updates. Regular firmware updates and vendor advisories should be monitored closely for patches addressing this vulnerability.