CVE-2018-20901 in cPanel
Summary
by MITRE
cPanel before 71.9980.37 allows Remote-Stored XSS in WHM Save Theme Interface (SEC-400).
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Analysis
by VulDB Data Team • 07/18/2020
The vulnerability identified as CVE-2018-20901 represents a significant security flaw in cPanel software versions prior to 71.9980.37, specifically affecting the WHM Save Theme Interface functionality. This issue enables remote attackers to inject malicious scripts into the system through a stored cross-site scripting vulnerability, creating a persistent threat vector that can compromise user sessions and potentially escalate privileges within the administrative interface. The vulnerability resides in the theme saving mechanism of WHM, which fails to properly sanitize user input before storing and rendering it within the web interface, thereby creating an environment where malicious payloads can be executed in the context of other users' browsers.
The technical exploitation of this vulnerability occurs through the improper handling of user-supplied data within the WHM theme interface. When administrators or users interact with the theme saving functionality, the system accepts input without adequate validation or sanitization processes, allowing malicious actors to embed javascript code or other malicious content that gets stored within the application's data store. This stored content is then subsequently rendered to other users who access the affected interface, making it a classic stored XSS vulnerability that can affect multiple users over time. The flaw aligns with CWE-79 which specifically addresses Cross-Site Scripting vulnerabilities, and more specifically CWE-80 which deals with improper neutralization of script-embedded characters in web pages, as the application fails to properly escape or filter user input before rendering it in the web interface.
The operational impact of CVE-2018-20901 extends beyond simple script execution, potentially enabling attackers to perform session hijacking, steal administrative credentials, manipulate user data, and gain unauthorized access to sensitive system information. The vulnerability affects the WHM (Web Host Manager) interface, which provides administrative controls for cPanel hosting environments, making it particularly dangerous as it could allow attackers to compromise entire hosting accounts or even entire servers depending on the scope of access granted to the compromised administrative interface. Attackers could leverage this vulnerability to execute commands on behalf of legitimate users, modify theme configurations, or redirect users to malicious sites, all while maintaining persistence within the target environment. The security implications align with ATT&CK technique T1566 which covers credential harvesting through phishing and social engineering, as the stored XSS could be used to capture administrative sessions or credentials.
Mitigation strategies for this vulnerability involve immediate patching of cPanel installations to version 71.9980.37 or later, which includes proper input sanitization and output encoding mechanisms for the WHM theme interface. Organizations should also implement additional defensive measures such as web application firewalls that can detect and block malicious script patterns, regular security auditing of administrative interfaces, and user education regarding the risks of interacting with untrusted content within administrative panels. Network segmentation and least privilege access controls can help limit the potential damage if exploitation occurs, while regular monitoring of web application logs can help detect suspicious activities related to theme modifications or unusual user behavior within the WHM interface. The vulnerability demonstrates the critical importance of input validation and output encoding in web applications, particularly within administrative interfaces where the potential impact of XSS attacks can be severe and far-reaching.