CVE-2017-18451 in cPanel
Summary
by MITRE
cPanel before 64.0.21 allows attackers to read a user's crontab file during a short time interval upon a cPAddon upgrade (SEC-257).
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Analysis
by VulDB Data Team • 07/19/2020
The vulnerability identified as CVE-2017-18451 affects cPanel versions prior to 64.0.21 and represents a critical privilege escalation and information disclosure flaw that exploits a timing window during cPAddon upgrades. This vulnerability allows attackers to read sensitive user crontab files through a race condition that occurs when the system temporarily grants elevated access permissions during the upgrade process. The flaw specifically manifests during the brief interval when cPAddon components are being updated, creating a window where unauthorized access to crontab files becomes possible. The vulnerability demonstrates a fundamental security weakness in how the system manages file permissions and access controls during software upgrade procedures, particularly when dealing with user-level scheduling information that typically requires elevated privileges to access.
The technical implementation of this vulnerability exploits a race condition between the cPAddon upgrade process and file system access controls. During the upgrade, the system temporarily modifies access permissions for crontab files, creating a window where attackers can read these files before the permissions are properly restored. This timing attack leverages the fact that crontab files contain scheduled tasks and potentially sensitive command execution information that could include credentials, system access tokens, or other confidential operational data. The vulnerability falls under CWE-362, which specifically addresses race conditions in security-critical operations, and demonstrates how improper synchronization of access controls during system maintenance operations can create exploitable conditions. The flaw represents a classic example of how upgrade and maintenance procedures can inadvertently introduce security gaps when access control mechanisms are not properly synchronized with system state changes.
The operational impact of this vulnerability extends beyond simple information disclosure, as crontab files often contain critical system automation commands that could include sensitive credentials, database access information, or other operational data that attackers could leverage for further compromise. When attackers can read these files during the upgrade window, they gain access to scheduled tasks that may execute with elevated privileges, potentially providing pathways to privilege escalation or lateral movement within the system. The vulnerability also represents a significant concern for compliance and audit requirements, as it allows unauthorized access to scheduled operations that should remain protected. This flaw particularly affects hosting environments where multiple users share the same cPanel instance, as attackers could potentially access other users' crontab files and extract sensitive operational information. The timing aspect of this vulnerability makes it particularly dangerous because it can be exploited repeatedly during upgrade windows, providing multiple opportunities for attackers to gather intelligence or escalate privileges.
Mitigation strategies for CVE-2017-18451 require immediate implementation of the vendor-provided patch to cPanel version 64.0.21 or later, which addresses the race condition by properly synchronizing access control modifications during upgrade operations. Organizations should also implement monitoring for upgrade processes and establish strict access controls for upgrade procedures to minimize the window of vulnerability. The remediation process should include verification that proper file permissions are maintained throughout the upgrade lifecycle and that access controls are properly restored immediately after upgrade completion. Security teams should conduct regular audits of scheduled tasks and crontab files to identify any unauthorized modifications or access patterns that may indicate exploitation attempts. Additionally, implementing network segmentation and access controls around cPanel management interfaces can limit the attack surface, while regular security assessments should verify that upgrade procedures maintain proper security boundaries. This vulnerability demonstrates the importance of considering security implications during system maintenance operations and aligns with ATT&CK techniques related to privilege escalation and credential access through system maintenance vulnerabilities.