CVE-2018-8712 in Webmin
Summary
by MITRE
An issue was discovered in Webmin 1.840 and 1.880 when the default Yes setting of "Can view any file as a log file" is enabled. As a result of weak default configuration settings, limited users have full access rights to the underlying Unix system files, allowing the user to read sensitive data from the local system (using Local File Include) such as the '/etc/shadow' file via a "GET /syslog/save_log.cgi?view=1&file=/etc/shadow" request.
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Analysis
by VulDB Data Team • 01/13/2020
The vulnerability identified as CVE-2018-8712 represents a critical privilege escalation flaw in Webmin versions 1.840 and 1.880 that stems from dangerously permissive default configuration settings. This issue exploits the default "Yes" setting for the "Can view any file as a log file" parameter, which creates an inherent security weakness that allows limited user accounts to gain unauthorized access to sensitive system files. The vulnerability specifically targets the syslog module's save_log.cgi component, where the lack of proper input validation and access controls enables attackers to manipulate file paths through the file parameter in the GET request. This misconfiguration effectively transforms a restricted user account into a system-level attacker capable of reading any file on the Unix filesystem that the Webmin process has access to, fundamentally undermining the principle of least privilege and creating a severe attack surface.
The technical exploitation of this vulnerability leverages a classic local file inclusion (LFI) attack pattern that maps directly to CWE-22, which describes improper limitation of a pathname to a restricted directory. The attack vector specifically targets the save_log.cgi script's handling of the file parameter, where user-supplied input is directly incorporated into file system operations without adequate sanitization or access control verification. When an attacker issues a request such as GET /syslog/save_log.cgi?view=1&file=/etc/shadow, the system processes this without validating whether the requested file path is within acceptable boundaries. This allows the attacker to traverse the filesystem and access sensitive files like /etc/shadow, which contains hashed password information for all system users, thereby providing a direct pathway to credential compromise and potential system takeover. The vulnerability demonstrates a fundamental failure in input validation and access control enforcement that aligns with ATT&CK technique T1078.1.1, which covers valid accounts with default passwords, though in this case it's about default configuration settings that create equivalent security weaknesses.
The operational impact of CVE-2018-8712 extends far beyond simple data theft, as it provides attackers with a complete pathway to system compromise and persistent access. The ability to read /etc/shadow directly enables password cracking attacks, while access to other system files can reveal configuration details, network settings, and potentially sensitive application data. This vulnerability can be exploited by attackers with minimal privileges, making it particularly dangerous in environments where multiple users have access to Webmin systems. The default nature of the vulnerability means that systems are inherently compromised upon installation without any additional configuration changes, creating a widespread risk across all affected Webmin deployments. Organizations that fail to address this vulnerability effectively create an environment where attackers can escalate privileges without requiring additional attack vectors or exploiting other weaknesses. The long-term implications include potential lateral movement within networks, persistence mechanisms that can survive system reboots, and the ability to establish backdoors or exfiltrate additional sensitive data from the compromised system.
Mitigation strategies for CVE-2018-8712 must address both the immediate configuration issue and broader security hygiene practices. The primary remediation involves changing the default "Can view any file as a log file" setting from Yes to No, which immediately eliminates the attack vector by preventing users from accessing arbitrary files through the syslog module. System administrators should also implement proper access controls and privilege management, ensuring that users only have access to the specific functions and files necessary for their roles. Regular security audits and configuration reviews are essential to identify similar default settings that may create security weaknesses. Additional protective measures include implementing network segmentation to limit access to Webmin interfaces, enforcing strong authentication mechanisms, and deploying intrusion detection systems to monitor for suspicious file access patterns. Organizations should also consider applying the latest Webmin patches and updates, as this vulnerability was addressed in subsequent releases. The incident underscores the importance of security by design principles and the critical need for organizations to regularly review and harden default configurations rather than relying on potentially insecure out-of-the-box settings that can be exploited by attackers with minimal technical expertise.