CVE-2018-20114 in DIR-818LW
Summary
by MITRE
On D-Link DIR-818LW Rev.A 2.05.B03 and DIR-860L Rev.B 2.03.B03 devices, unauthenticated remote OS command execution can occur in the soap.cgi service of the cgibin binary via an "&&" substring in the service parameter. NOTE: this issue exists because of an incomplete fix for CVE-2018-6530.
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Analysis
by VulDB Data Team • 04/25/2020
The vulnerability described in CVE-2018-20114 represents a critical remote command execution flaw affecting D-Link DIR-818LW and DIR-860L wireless routers. This issue specifically targets the soap.cgi service within the cgibin binary of these network devices, creating a pathway for unauthenticated attackers to execute arbitrary operating system commands remotely. The vulnerability stems from insufficient input validation within the service parameter handling mechanism, where the system fails to properly sanitize user-supplied input containing the "&&" substring. This particular substring sequence enables attackers to chain commands and bypass security controls that would normally prevent command injection attacks. The flaw is particularly concerning as it affects multiple D-Link router models within the same product line, indicating a systemic issue in the firmware implementation rather than an isolated incident. The vulnerability exists because the device manufacturers implemented an incomplete fix for a previously discovered vulnerability CVE-2018-6530, which demonstrates poor vulnerability management practices and inadequate regression testing.
The technical implementation of this vulnerability occurs at the web service layer where the soap.cgi script processes incoming requests without proper sanitization of the service parameter. When an attacker submits a malicious payload containing the "&&" sequence, the system interprets this as a command separator and executes additional commands beyond the intended functionality. This type of vulnerability falls under CWE-78 which specifically addresses OS Command Injection, and aligns with ATT&CK technique T1059.001 for command and scripting interpreter. The attack vector requires no authentication credentials, making it particularly dangerous as it allows any remote attacker to exploit the device. The incomplete fix for CVE-2018-6530 suggests that the original mitigation was insufficiently comprehensive, leaving residual attack surfaces that could be leveraged by threat actors. The use of the "&&" substring is a common technique in command injection attacks as it allows attackers to append additional commands to the original execution flow, potentially enabling full system compromise.
The operational impact of this vulnerability extends far beyond simple unauthorized access to router configuration. An attacker who successfully exploits this vulnerability can gain complete control over the affected router, potentially using it as a pivot point to access internal network resources. The compromised device could serve as a launching pad for further attacks against connected systems, including the ability to redirect traffic, modify network settings, or even establish persistent backdoors. Network administrators face significant risks as these devices are typically deployed in home and small office environments where they may not be regularly updated or monitored for security issues. The vulnerability could enable attackers to create persistent access to internal networks, potentially leading to data exfiltration, man-in-the-middle attacks, or the establishment of botnet nodes. The lack of authentication requirements means that attackers can exploit this vulnerability at scale without needing to guess credentials or perform additional reconnaissance.
Mitigation strategies for this vulnerability require immediate action from network administrators to address the root cause. The primary recommendation involves applying firmware updates from D-Link that contain proper input sanitization for the soap.cgi service and the service parameter handling. Organizations should also implement network segmentation to limit the exposure of these devices to untrusted networks and consider deploying intrusion detection systems that can identify suspicious command execution patterns. Network access controls should be configured to restrict access to the affected services and ports, particularly those used by the soap.cgi interface. Security monitoring should include detection of unusual command execution patterns and the presence of "&&" sequences in service parameters. Additionally, network administrators should consider disabling unnecessary services and features on these devices to reduce the attack surface. The vulnerability highlights the importance of comprehensive vulnerability management processes and the need for thorough regression testing when implementing security fixes. Organizations should also implement regular security assessments of network infrastructure to identify similar vulnerabilities that may exist in other network devices and firmware implementations.