CVE-2019-9706 in Vixie cron
Summary
by MITRE
Vixie Cron before the 3.0pl1-133 Debian package allows local users to cause a denial of service (use-after-free and daemon crash) because of a force_rescan_user error.
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Analysis
by VulDB Data Team • 07/31/2023
The vulnerability identified as CVE-2019-9706 affects Vixie Cron versions prior to 3.0pl1-133 in Debian package distributions, representing a critical security flaw that enables local attackers to execute denial of service attacks through use-after-free conditions. This vulnerability specifically manifests when the cron daemon encounters a force_rescan_user error, creating a scenario where freed memory locations are accessed, leading to unpredictable behavior and ultimately causing the daemon to crash. The flaw exists within the cron daemon's memory management mechanisms, where improper handling of user scanning operations results in memory corruption that can be exploited by local users with minimal privileges.
The technical nature of this vulnerability aligns with CWE-416, which describes use-after-free conditions in software systems, and represents a classic memory safety issue that has been prevalent in Unix-like systems for decades. When the force_rescan_user function processes user information, it fails to properly manage memory allocation and deallocation sequences, allowing attackers to manipulate the cron daemon's operation. The daemon's failure to validate or properly handle user data during rescan operations creates a window where freed memory blocks become accessible, enabling malicious code execution or system instability. This type of vulnerability falls under the ATT&CK technique T1499.004 for network denial of service, though in this case the attack vector operates locally rather than over network protocols.
The operational impact of CVE-2019-9706 extends beyond simple daemon crashes, as it can disrupt critical system maintenance schedules and automated tasks that depend on cron services. System administrators rely on cron for regular backups, log rotations, security updates, and other essential operations, making this vulnerability particularly dangerous in production environments. When the cron daemon crashes due to this flaw, scheduled tasks may fail to execute, potentially leading to data loss, security gaps, and system instability. The vulnerability's local nature means that attackers do not require network access or elevated privileges, making it an attractive target for malicious actors who wish to disrupt system operations without detection. Organizations using affected Debian-based systems face significant risk, as the vulnerability can be exploited by any local user with minimal system access.
Mitigation strategies for CVE-2019-9706 primarily focus on updating to the patched version of the Vixie Cron package, specifically version 3.0pl1-133 or later, which addresses the memory management issues in the force_rescan_user function. System administrators should implement immediate patching procedures across all affected systems, particularly those running Debian-based distributions such as Ubuntu, Debian, or derivatives. Additional protective measures include implementing proper access controls to limit local user privileges, monitoring cron daemon behavior for unusual patterns, and ensuring that automated systems regularly verify cron service health. Security teams should also consider implementing intrusion detection systems that can identify potential exploitation attempts and maintain comprehensive system logging to track any daemon crashes or memory-related errors that might indicate exploitation of this vulnerability.