CVE-2018-20935 in cPanel
Summary
by MITRE
cPanel before 70.0.23 allows stored XSS in via a WHM "Reset a DNS Zone" action (SEC-412).
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Analysis
by VulDB Data Team • 07/18/2020
The vulnerability CVE-2018-20935 represents a critical stored cross-site scripting flaw in cPanel versions prior to 70.0.23, specifically affecting the WHM (Web Host Manager) interface. This vulnerability resides within the "Reset a DNS Zone" functionality, making it particularly dangerous as it allows attackers to inject malicious scripts that persist in the system and affect multiple users. The flaw falls under CWE-79 which classifies it as a classic stored XSS vulnerability where malicious input is stored on the server and then served to unsuspecting users.
The technical implementation of this vulnerability occurs when an attacker exploits the DNS zone reset functionality in WHM, which fails to properly sanitize user input. When a user interacts with the affected interface, particularly when viewing DNS zone information or performing zone resets, the malicious scripts stored in the database execute in the context of other users' browsers. This creates a persistent threat where the injected code can perform actions such as stealing session cookies, redirecting users to malicious sites, or executing unauthorized operations on behalf of the victims. The vulnerability is particularly concerning because WHM interfaces are typically accessed by system administrators and hosting providers who possess elevated privileges, making the potential impact significantly greater than in standard user interfaces.
Operationally, this vulnerability creates substantial risk for hosting environments and web infrastructure management systems. Attackers can leverage this flaw to compromise administrator sessions, potentially gaining complete control over hosting accounts, DNS configurations, and associated services. The stored nature of the XSS means that the malicious code remains active until manually removed from the system, creating a persistent threat vector that can affect numerous users over extended periods. This vulnerability directly aligns with ATT&CK technique T1059.006 for command and scripting interpreter, as the stored scripts can execute arbitrary commands or access sensitive data within the compromised browser sessions.
The impact extends beyond immediate exploitation as it can facilitate more sophisticated attacks including credential theft, privilege escalation, and data exfiltration. System administrators who perform DNS zone operations become potential attack vectors for broader network compromise, especially in shared hosting environments where multiple clients are managed through the same cPanel instance. Organizations using affected cPanel versions face increased risk of service disruption, data breaches, and regulatory compliance violations. The vulnerability demonstrates the critical importance of input validation and output encoding in web applications, particularly in administrative interfaces where the consequences of successful exploitation are most severe. Organizations should implement immediate patching measures and consider monitoring for suspicious DNS zone activities as part of their incident response protocols.
Mitigation strategies include upgrading to cPanel version 70.0.23 or later, which contains the necessary fixes for this vulnerability. Additionally, implementing proper input sanitization and output encoding mechanisms can help prevent similar issues in other applications. Security monitoring should be enhanced to detect unusual DNS zone reset activities, and regular security assessments of administrative interfaces should be conducted. The vulnerability highlights the need for comprehensive security testing including penetration testing and code reviews, particularly focusing on user input handling in privileged interfaces. Organizations should also consider implementing web application firewalls and security headers to provide additional protection layers against such attacks.