CVE-2026-11556: Tenda F451 Command Injection Vulnerability (CVSS 8.8)

Technical summary

CVE-2026-11556 exploits improper input validation in the Tenda F451 web interface component responsible for MAC address configuration. The formWriteFacMac function fails to sanitize the 'mac' parameter before passing it to OS-level commands, enabling shell command injection via metacharacters. The attack leverages CWE-77 (Improper Neutralization of Special Elements) and CWE-78 (OS Command Injection), allowing an authenticated user to break out of intended command boundaries and execute arbitrary code with device privileges. Network-accessible delivery combined with low complexity and high impact severity creates a significant risk profile.

Business impact

Compromise of a Tenda F451 device can enable attackers to intercept, modify, or block network traffic for all connected users. Routers often manage sensitive network segments, and full device control allows lateral movement into corporate or home networks. Affected organizations face data exfiltration risks, man-in-the-middle attack vectors, and potential pivot points for ransomware deployment. For managed service providers or small businesses relying on these devices, exploitation could trigger compliance violations and customer trust erosion.

Affected systems

Tenda F451 firmware versions 1.0.0.7 and 1.0.0.9 are explicitly affected. The vulnerability resides in the web management interface, so any instance with remote management enabled or accessible from the LAN is at risk. Organizations should inventory all Tenda F451 deployments and verify installed firmware versions against these two impacted releases.

Exploitability

Exploitation requires valid authentication credentials to access the web management interface, which raises the barrier compared to unauthenticated flaws. However, default credentials, weak passwords, or credential compromise via phishing make this a practical attack vector. Public exploit code availability heightens risk—adversaries with network access can weaponize attacks quickly. The low complexity of exploitation (simple parameter manipulation) means even unsophisticated attackers can succeed once authenticated.

Remediation

Firmware updates addressing this vulnerability must be obtained from Tenda's support portal. Organizations should verify against official Tenda advisories to confirm patch availability for versions 1.0.0.7 and 1.0.0.9. Until patches are available, mitigate risk by restricting web management interface access to trusted IP ranges, disabling remote management, enforcing strong authentication, and monitoring for suspicious command patterns in device logs.

Patch guidance

Contact Tenda support or consult their official security advisories for patched firmware versions targeting the F451 model. Verify patch availability before deploying—confirm that any released update explicitly addresses CVE-2026-11556. Deploy patches during maintenance windows to avoid network disruption. After patching, validate that the device reboots successfully and that web interface functionality is restored. For devices without available patches, implement strict network segmentation and access controls as interim protection.

Detection guidance

Monitor web server logs on affected Tenda F451 devices for suspicious POST requests to /goform/WriteFacMac with unusual characters (backticks, pipes, semicolons, ampersands, or command substitution syntax) in the 'mac' parameter. Alert on successful command executions following such requests. Network-level detection can identify lateral communication from compromised routers to internal systems. Behavioral signals include unexpected outbound connections from the device, DNS query patterns inconsistent with normal operation, or traffic to known malicious infrastructure.

Why prioritize this

This vulnerability merits rapid remediation because: (1) firmware updates exist or are imminent, making patching achievable; (2) the CVSS 8.8 HIGH severity reflects significant confidentiality, integrity, and availability impact; (3) public exploit availability accelerates attack adoption; (4) routers are critical network infrastructure—compromise enables broad organizational compromise; (5) authentication requirement alone does not justify delay given default credential risks and insider threat scenarios. Prioritize patching over lower-severity issues.

Risk score, explained

CVSS 3.1 score of 8.8 (HIGH) reflects the combination of network-accessible attack vector, low attack complexity, and requirement for low privilege (authenticated user). The vector notation (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) assigns maximum impact across confidentiality, integrity, and availability—a compromised router can read all traffic, modify communications, and be shut down. The authentication requirement (PR:L) prevents a perfect 9.9 score, but does not diminish the severity given credential exposure risks and the device's centralized role in network security.

Frequently asked questions