Tenda 4G03 Pro Improper Access Control Vulnerability (CVE-2026-5526)

A security vulnerability, identified as CVE-2026-5526, affects the Tenda 4G03 Pro router, specifically versions up to 1.0/1.1/04.03.01.53/192.168.0.1. The flaw resides within an unspecified function of the /bin/httpd file, leading to improper access controls. A remote attacker could exploit this vulnerability, potentially gaining unauthorized access to the device. Publicly available exploits exist, increasing the risk of exploitation. This issue was reported on April 4, 2026, and poses a significant threat due to the ease of remote exploitation.

Attack Chain

1. Attacker identifies a Tenda 4G03 Pro router with a publicly accessible web interface.
2. The attacker crafts a malicious HTTP request targeting the /bin/httpd file.
3. The malicious request exploits the improper access control vulnerability (CVE-2026-5526).
4. The router’s /bin/httpd process improperly handles the request, bypassing access controls.
5. The attacker gains unauthorized access to sensitive functionalities of the router.
6. The attacker modifies router configurations, such as DNS settings or firewall rules.
7. The attacker could potentially use the compromised router as a pivot point for further network attacks.

Impact

Successful exploitation of CVE-2026-5526 could allow attackers to remotely compromise Tenda 4G03 Pro routers. This can lead to unauthorized access to the device’s configuration, modification of settings, or use of the router as a stepping stone for further attacks within the network. Given the availability of public exploits, unpatched devices are at significant risk. While the exact number of affected devices is unknown, the widespread use of Tenda routers makes this a potentially significant issue.

Recommendation

• Monitor web server logs for suspicious requests targeting /bin/httpd using the provided Sigma rule.
• Apply available firmware updates or patches from Tenda to address CVE-2026-5526 as soon as they are released.
• Implement network segmentation to limit the impact of a compromised router.
• Enforce strong password policies for router administration to prevent unauthorized access.
• Review and update firewall rules to restrict access to the router’s web interface from untrusted networks.
• Deploy the provided Sigma rule to detect suspicious process execution originating from the web server process.