CVE-2018-20951 in cPanel
Summary
by MITRE
cPanel before 68.0.27 allows self XSS in WHM Spamd Startup Config (SEC-387).
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Analysis
by VulDB Data Team • 07/18/2020
The vulnerability identified as CVE-2018-20951 represents a self-XSS (Cross-Site Scripting) flaw within the cPanel web hosting control panel software. This issue specifically affects versions prior to 68.0.27 and occurs within the WHM Spamd Startup Configuration component of the administrative interface. The vulnerability stems from insufficient input validation and output sanitization mechanisms that fail to properly escape or filter user-controllable data before rendering it within the web interface. This particular flaw allows authenticated attackers with administrative privileges to inject malicious scripts that execute within the context of the WHM interface, potentially compromising the security of the entire hosting environment.
The technical implementation of this vulnerability involves the improper handling of user-supplied parameters within the Spamd Startup Configuration section of WHM. When administrators configure spam filtering parameters through this interface, the system fails to adequately sanitize input values before displaying them back to the user. This creates an environment where malicious payloads can be stored and subsequently executed when the configuration page is accessed again. The self-XSS nature means that the vulnerability affects the victim who is authenticated as an administrator, making it particularly dangerous as it can be exploited by attackers who have already gained administrative access or by compromising legitimate administrative sessions.
The operational impact of this vulnerability extends beyond simple script execution, as it can potentially enable attackers to escalate privileges, steal administrative sessions, or manipulate critical system configurations. An attacker could craft malicious payloads that redirect administrators to phishing sites, steal session cookies, or modify spam filtering rules to allow malicious emails through the system. The vulnerability is particularly concerning in shared hosting environments where multiple administrators may be working with the same control panel, as it could allow for privilege escalation or unauthorized access to sensitive hosting configurations. This flaw directly impacts the integrity of the WHM administrative interface and can compromise the security posture of entire hosting infrastructure.
Mitigation strategies for CVE-2018-20951 should prioritize immediate patching to cPanel version 68.0.27 or later, which includes proper input validation and output sanitization measures. Organizations should implement comprehensive monitoring of WHM administrative sessions and conduct regular security audits of control panel configurations. The vulnerability aligns with CWE-79 which categorizes cross-site scripting flaws, and can be mapped to ATT&CK technique T1059.005 for command and scripting interpreter. Additional defensive measures include implementing strict input validation at all entry points, enabling Content Security Policy headers, and conducting regular security training for administrators to recognize and avoid potentially malicious configuration inputs. Network segmentation and privileged access controls should also be enforced to limit the potential impact of successful exploitation attempts.