CWE-330: Use of Insufficiently Random Values - CVE-2015-5987

DNS queries originating from the Belkin N600, such as those to resolve the names of firmware update and NTP servers, use predictable TXIDs that start at 0x0002 and increase incrementally. An attacker with the ability to spoof DNS responses can cause the router to contact incorrect or malicious hosts under the attacker's control.

CWE-319: Cleartext Transmission of Sensitive Information

Belkin uses HTTP by default for checking and transmitting firmware update information to vulnerable routers. An attacker capable of conducting man-in-the-middle attacks can manipulate traffic to block updates or inject arbitrary files.

CWE-255: Credentials Management - CVE-2015-5988

Belkin N600 by default does not set a password for the web management interface. A local area network (LAN) attacker can gain privileged access to the web management interface or leverage the default absence of credentials in remote attacks such as cross-site request forgery.

CWE-603: Use of Client-Side Authentication - CVE-2015-5989

When a password is implemented in the Belkin N600 web management interface, authorization is enforced client-side by the browser. By intercepting packets from the embedded server containing the strings "LockStatus": "1" and "Login_Success": "0" and modifying the values to "2" and "1" respectively, an attacker can bypass authentication and gain full, privileged access to restricted pages of the web management interface.

CWE-352: Cross-Site Request Forgery (CSRF) - CVE-2015-5990

Belkin N600 routers contain a global cross-site request forgery (CSRF) vulnerability. An attacker can perform actions with the same permissions as a victim user, provided the victim has an active session and is induced to trigger the malicious request. Note that in default configurations lacking password protection, an attacker can establish an active session as part of an attack and does not require a victim to be logged in.

The CVSS score below describes CVE-2015-5990.

A remote, unauthenticated attacker may be able to spoof DNS responses to cause vulnerable devices to contact attacker-controlled hosts or induce an authenticated user into making an unintentional request to the web server that will be treated as an authentic request. A LAN-based attacker can bypass authentication to take complete control of vulnerable devices.

The CERT/CC is currently unaware of a practical solution to this problem. Until these vulnerabilities are addressed, users should consider the following workarounds.

Restrict access and use strong passwords

As a general good security practice, only allow trusted hosts to connect to the LAN. Implement strong passwords for WiFi and for the web management interface. While passwords do not provide any additional security against LAN-based attackers due to the authentication bypass vulnerability, passwords can help to prevent blind guessing attempts that would establish sessions for CSRF attacks. LAN hosts should not browse the Internet while the web management interface has an active session in a browser tab.

Note that there are no practical workarounds for the DNS spoofing or firmware over HTTP issues, as general users are unlikely to be able to monitor traffic entering the router's WAN port.