CVE-2017-18393 in cPanel
Summary
by MITRE
cPanel before 68.0.15 does not block a username of postmaster, which might allow reception of private e-mail (SEC-326).
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Analysis
by VulDB Data Team • 07/18/2020
The vulnerability identified as CVE-2017-18393 affects cPanel versions prior to 68.0.15 and relates to improper username validation within the email handling subsystem. This flaw specifically concerns the restriction of the postmaster username, which is a well-known system account used for handling mail server administrative messages. The vulnerability stems from cPanel's failure to properly validate and block the use of the postmaster username during user account creation or email configuration processes, creating a potential security risk that could allow unauthorized access to private email communications.
The technical implementation of this vulnerability involves cPanel's email management interface where user accounts are created and configured. When a user attempts to create an email account using the postmaster username, the system fails to reject this request despite the postmaster account being reserved for system-level mail operations. This creates a scenario where an attacker could potentially intercept or access private email communications that should remain restricted to system administrators. The flaw represents a failure in input validation and access control mechanisms, specifically allowing privilege escalation through email account manipulation.
The operational impact of this vulnerability extends beyond simple email access issues and could enable sophisticated attack vectors within email infrastructure. An attacker who successfully exploits this vulnerability could potentially intercept system-generated emails, access sensitive administrative communications, or manipulate email routing for malicious purposes. The vulnerability particularly affects organizations that rely on cPanel for email hosting services, as it undermines the security boundaries between regular user accounts and system administrative functions. This could lead to data breaches, privilege escalation attacks, and potential compromise of the entire email infrastructure.
Security controls and mitigations for this vulnerability primarily involve updating to cPanel version 68.0.15 or later, which implements proper validation of the postmaster username. Organizations should also conduct comprehensive audits of existing email accounts to ensure no unauthorized postmaster accounts have been created. The fix aligns with common security practices for preventing privilege escalation through improper input validation and access control enforcement. This vulnerability maps to CWE-20, which describes improper input validation, and could be categorized under ATT&CK technique T1078 for valid accounts, as it enables unauthorized access through legitimate system accounts. Network administrators should implement monitoring for unusual email account creation patterns and establish proper access controls for email administrative functions to prevent exploitation of similar vulnerabilities in other components of the email infrastructure.