CVE-2018-20895 in cPanel
Summary
by MITRE
In cPanel before 71.9980.37, API tokens retain ACLs after those ACLs are removed from the corresponding accounts (SEC-393).
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Analysis
by VulDB Data Team • 07/18/2020
The vulnerability identified as CVE-2018-20895 represents a critical access control flaw in cPanel software versions prior to 71.9980.37. This issue stems from a persistent authorization problem where API tokens continue to maintain their original access control lists even after the corresponding user accounts have had those ACLs removed. The vulnerability affects the core authentication and authorization mechanisms of cPanel, which is widely used by hosting providers and system administrators to manage web hosting accounts and server resources. This flaw creates a scenario where revoked permissions remain active, potentially allowing unauthorized access to resources that should no longer be available to specific users.
The technical nature of this vulnerability aligns with CWE-284, which addresses improper access control, and specifically relates to the improper management of access control lists within the API token system. When administrators remove or modify access permissions for user accounts, the system fails to properly invalidate existing API tokens that were generated while those permissions were active. This creates a persistent security risk where deleted or modified access controls are effectively bypassed through the use of previously issued tokens. The flaw operates at the intersection of identity management and access control enforcement, where the token-based authentication system does not properly synchronize with the account permission state changes.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it undermines the fundamental security model of cPanel's access control system. System administrators who believe they have revoked access to specific resources through account modifications may find that API tokens continue to grant access to those resources, potentially leading to data breaches, unauthorized system modifications, or privilege abuse. This issue is particularly concerning in shared hosting environments where multiple users may have varying levels of access, and where the security of one user's account can impact others. The vulnerability can be exploited by malicious actors who obtain valid API tokens, potentially allowing them to maintain access to resources even after legitimate access has been revoked. The persistence of these access rights creates a window where unauthorized activities can occur without detection, as the system appears to function normally while maintaining compromised access paths.
Mitigation strategies for this vulnerability should include immediate patching to cPanel version 71.9980.37 or later, which resolves the ACL synchronization issue in API token management. Organizations should also implement proactive monitoring of API token usage and conduct regular audits of access control configurations to identify and revoke stale tokens. Security teams should establish policies for token lifecycle management, including automatic token expiration and periodic token rotation. The vulnerability demonstrates the importance of maintaining synchronization between authentication and authorization systems, and highlights the need for comprehensive access control reviews. Additionally, implementing principle of least privilege practices and regular security assessments can help minimize the impact of such persistent access control flaws. Organizations should also consider implementing additional monitoring and alerting mechanisms to detect unusual API token usage patterns that might indicate exploitation of this vulnerability. The remediation process should include verification that all existing API tokens have been properly invalidated and that new tokens are generated with correct ACL assignments, ensuring that access control changes are immediately enforced across all authentication mechanisms.