CVE-2012-6110 in Bcron Exec
Summary
by MITRE
bcron-exec in bcron before 0.10 does not close file descriptors associated with temporary files when running a cron job, which allows local users to modify job files and send spam messages by accessing an open file descriptor.
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Analysis
by VulDB Data Team • 03/18/2019
The vulnerability identified as CVE-2012-6110 affects the bcron cron daemon version 0.10 and earlier, specifically within the bcron-exec component responsible for executing scheduled jobs. This flaw represents a critical security issue that stems from improper resource management during job execution processes. The vulnerability arises from the daemon's failure to properly close file descriptors associated with temporary files created during cron job execution, creating persistent access points that can be exploited by local attackers.
The technical root cause of this vulnerability can be categorized under CWE-1173, which addresses improper handling of file descriptors and resource management in Unix-like systems. When bcron-exec processes a cron job, it creates temporary files to store job execution data but fails to close the file descriptors associated with these temporary files. This oversight allows malicious users to maintain access to these file descriptors even after the initial job execution has completed. The persistent file descriptor access enables attackers to manipulate the contents of these temporary files, effectively gaining the ability to modify cron job configurations and inject malicious commands.
From an operational perspective, this vulnerability creates a significant attack surface for local privilege escalation and persistent system compromise. An attacker with local access can exploit this flaw to modify cron job files, potentially injecting commands that execute with elevated privileges or redirect system resources for malicious purposes. The vulnerability is particularly concerning because it allows for the creation of spam messages through manipulation of the cron job execution environment, as the attacker can modify job parameters to send unwanted communications or perform other malicious activities.
The attack vector for this vulnerability is relatively straightforward, requiring only local system access and knowledge of the bcron execution process. Attackers can leverage the open file descriptors to inject malicious code into cron jobs or modify existing job parameters to redirect system resources. This vulnerability aligns with ATT&CK technique T1053.003, which covers scheduled task/job manipulation, and T1068, which addresses local privilege escalation through improper resource handling. The impact extends beyond simple spam generation to potential system compromise, as attackers can escalate privileges by modifying system cron jobs or creating persistent backdoors.
Mitigation strategies for this vulnerability include immediate patching of affected bcron installations to version 0.10 or later, where the file descriptor management has been corrected. System administrators should also implement proper file descriptor management practices and regularly audit cron job configurations to identify unauthorized modifications. Additionally, monitoring for unusual cron job execution patterns and implementing strict access controls on cron job directories can help detect exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper resource management in system daemons and the potential consequences of inadequate file descriptor handling in security-sensitive applications. Organizations should ensure that all system services properly close file descriptors and temporary file handles to prevent similar vulnerabilities from being exploited in other components of their infrastructure.