CVE-2017-9100 in DIR-600M
Summary
by MITRE
login.cgi on D-Link DIR-600M devices with firmware 3.04 allows remote attackers to bypass authentication by entering more than 20 blank spaces in the password field during an admin login attempt.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/03/2020
The vulnerability identified as CVE-2017-9100 affects D-Link DIR-600M wireless routers running firmware version 3.04 and potentially other affected models within the DIR-600 series. This authentication bypass flaw exists in the login.cgi web interface component that handles administrative login requests. The vulnerability represents a classic input validation weakness that demonstrates poor security implementation in network device firmware design. The affected devices are commonly deployed in residential and small office environments where they serve as primary network gateways, making them attractive targets for malicious actors seeking unauthorized access to network infrastructure. This type of vulnerability falls under the category of weak authentication mechanisms that can lead to complete network compromise when exploited successfully.
The technical flaw manifests in the password field validation logic within the login.cgi script where the system fails to properly sanitize or validate input containing excessive whitespace characters. Specifically when an attacker enters more than twenty consecutive blank spaces in the password field during administrative login attempts, the authentication mechanism incorrectly processes this input and grants access to the administrative interface. This behavior occurs because the firmware does not implement proper input length validation or whitespace trimming before performing authentication checks. The vulnerability stems from inadequate boundary condition testing and insufficient input sanitization routines that should have been implemented during the firmware development lifecycle. According to CWE classification, this vulnerability maps to CWE-20: Improper Input Validation, which encompasses issues where input validation is insufficient to prevent malicious input from being processed by the application. The flaw essentially allows for a buffer overflow condition or input manipulation that bypasses the intended authentication flow, enabling unauthorized administrative access to the device.
The operational impact of this vulnerability is significant as it provides remote attackers with complete administrative control over affected D-Link routers without requiring knowledge of valid credentials. Once exploited, attackers can modify network settings, change administrator passwords, install malicious firmware, monitor network traffic, and potentially use the compromised device as a pivot point for attacking other systems within the local network. The vulnerability is particularly dangerous because it can be exploited remotely over the internet without any prior authentication or physical access to the device. This type of attack vector aligns with ATT&CK technique T1078.004: Valid Accounts - SSH, where unauthorized access is achieved through manipulation of authentication mechanisms rather than credential theft or brute force attacks. Network administrators who are unaware of this vulnerability may inadvertently leave their networks exposed to attacks that could result in complete network compromise, data exfiltration, or use as a launching point for further attacks against connected systems.
Mitigation strategies for this vulnerability should begin with immediate firmware updates from D-Link, as the company has released patches addressing this specific authentication bypass flaw. Organizations should implement network segmentation to limit the exposure of these devices and consider disabling remote administration access where possible. Network monitoring should be enhanced to detect unusual login patterns or authentication attempts that might indicate exploitation attempts. Security teams should also verify that administrative interfaces are not accessible from untrusted networks and consider implementing additional authentication layers such as two-factor authentication or certificate-based access controls. The vulnerability demonstrates the importance of proper input validation and boundary condition testing in embedded systems, which should be addressed through comprehensive security testing during the development lifecycle. According to NIST SP 800-53 security controls, this issue highlights the need for access control mechanisms and input validation procedures to prevent unauthorized access to network devices. Regular security assessments of network infrastructure, including inventory tracking of all connected devices and their firmware versions, should be maintained to identify and remediate similar vulnerabilities before they can be exploited by malicious actors.