CVE-2018-6211 in DIR-620
Summary
by MITRE
On D-Link DIR-620 devices with a certain customized (by ISP) variant of firmware 1.0.3, 1.0.37, 1.3.1, 1.3.3, 1.3.7, 1.4.0, and 2.0.22, OS command injection is possible as a result of incorrect processing of the res_buf parameter to index.cgi.
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Analysis
by VulDB Data Team • 02/20/2020
The vulnerability CVE-2018-6211 represents a critical operating system command injection flaw affecting D-Link DIR-620 wireless routers running specific firmware versions. This issue manifests in customized firmware variants deployed by internet service providers, creating a significant security risk for network infrastructure. The vulnerability stems from improper input validation within the web interface's handling of the res_buf parameter in the index.cgi script, which allows remote attackers to execute arbitrary commands on the affected devices.
The technical exploitation occurs through the manipulation of the res_buf parameter, which is processed without adequate sanitization or validation measures. This flaw falls under CWE-77, which specifically addresses command injection vulnerabilities where user-supplied data is directly incorporated into operating system commands. The vulnerability enables attackers to bypass authentication mechanisms and execute commands with the privileges of the web server process, potentially leading to complete system compromise. The affected firmware versions 1.0.3, 1.0.37, 1.3.1, 1.3.3, 1.3.7, 1.4.0, and 2.0.22 all share this common input processing flaw, making them susceptible to the same exploitation techniques.
The operational impact of this vulnerability extends beyond simple command execution, as it allows attackers to gain persistent access to the affected network infrastructure. Through the command injection, adversaries can modify router configurations, establish backdoors, monitor network traffic, or even redirect traffic to malicious destinations. The vulnerability is particularly concerning in ISP-deployed environments where these routers serve as primary network access points for residential customers. Attackers could leverage this weakness to create persistent footholds within networks, potentially affecting multiple users connected through the compromised router. The attack vector requires no authentication, making it particularly dangerous as it can be exploited remotely without prior access credentials.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059.001, which covers command and script injection through operating system interfaces. The exploitation process typically involves crafting malicious payloads that are passed through the vulnerable res_buf parameter, allowing attackers to execute shell commands directly on the router's operating system. Mitigation strategies should focus on firmware updates provided by D-Link, network segmentation to limit the impact of compromised devices, and monitoring for unusual command execution patterns. Organizations should also implement network access controls and regularly audit their router configurations to identify and remediate similar vulnerabilities in other network equipment. The vulnerability demonstrates the importance of proper input validation and the potential risks associated with customized firmware deployments that may not receive timely security updates.