CVE-2017-14609 in Kannel
Summary
by MITRE
The server daemons in Kannel 1.5.0 and earlier create a PID file after dropping privileges to a non-root account, which might allow local users to kill arbitrary processes by leveraging access to this non-root account for PID file modification before a root script executes a "kill `cat /pathname`" command, as demonstrated by bearerbox.
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Analysis
by VulDB Data Team • 12/29/2022
The vulnerability identified as CVE-2017-14609 affects Kannel versions 1.5.0 and earlier, specifically targeting the server daemon components including bearerbox. This issue represents a privilege escalation flaw that exploits the timing window between privilege dropping and process management operations. The vulnerability occurs within the daemon startup sequence where the server creates a PID file while still operating with elevated privileges before transitioning to a non-root user account. This creates a window of opportunity for local attackers who have access to the non-root account to manipulate the PID file contents, potentially leading to arbitrary process termination.
The technical flaw stems from improper privilege management and race condition exploitation within the Kannel daemon initialization process. When the server daemon starts, it first creates a PID file containing its process identifier while still maintaining root privileges. Following this, the daemon drops privileges to a non-root user account for security purposes. However, the PID file remains accessible to the non-root user, creating a critical timing gap. During this window, an attacker with access to the non-root account can modify the PID file contents to contain the process identifier of a target process. When a root script subsequently executes a command like "kill `cat /pathname`", it inadvertently terminates the process specified in the manipulated PID file rather than the intended daemon process, demonstrating a classic race condition vulnerability.
The operational impact of this vulnerability is significant for systems running Kannel services, particularly those exposed to local users or compromised accounts. An attacker with local access to the non-root account used by the Kannel daemon can leverage this flaw to escalate privileges or disrupt system operations by terminating critical processes. The vulnerability affects the integrity and availability of the communication services provided by Kannel, potentially leading to service disruption or unauthorized access to SMS gateway functionality. This issue is particularly dangerous in environments where Kannel serves as a core communication infrastructure component, as it could be exploited to gain unauthorized control over messaging services or to cause denial of service conditions that impact legitimate users.
This vulnerability aligns with CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and CWE-284 (Improper Access Control) categories, representing a race condition where multiple processes or threads access shared resources without proper synchronization mechanisms. The flaw also relates to ATT&CK technique T1068 (Local Privilege Escalation) and T1489 (Service Stop) as it enables attackers to manipulate process execution and potentially escalate privileges through process termination. The root cause demonstrates poor privilege management practices and inadequate security controls during process initialization. Organizations should implement immediate mitigations including updating to Kannel versions 1.5.1 or later, which address this vulnerability through proper privilege management and PID file handling. Additionally, system administrators should review and restrict access to non-root accounts used by daemon processes, implement proper file permissions for PID files, and ensure that privilege dropping occurs before any file creation operations to prevent similar race conditions from occurring in other software components.