CVE-1999-0768 in Cron
Summary
by MITRE
Buffer overflow in Vixie Cron on Red Hat systems via the MAILTO environmental variable.
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Analysis
by VulDB Data Team • 10/13/2024
The vulnerability identified as CVE-1999-0768 represents a critical buffer overflow flaw within the Vixie Cron daemon implementation on Red Hat Linux systems. This issue specifically manifests when the MAILTO environment variable is processed during cron job execution, creating a scenario where malicious input can exceed the allocated buffer space and overwrite adjacent memory regions. The vulnerability stems from inadequate input validation and bounds checking within the cron daemon's handling of environment variables, particularly those related to email notifications for scheduled tasks. The flaw exists in the version of cron distributed with Red Hat systems, making it a widespread concern across numerous Unix-like operating systems that utilize this particular implementation. This vulnerability demonstrates a classic security weakness where improper handling of user-supplied data leads to potential arbitrary code execution or system compromise.
The technical exploitation of this buffer overflow occurs when an attacker crafts a specially formatted MAILTO environment variable that exceeds the predetermined buffer size allocated for storing email addresses or notification parameters. When the cron daemon processes this malformed input, the excessive data overflows into adjacent memory locations, potentially corrupting critical program state information, return addresses, or other executable code. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, where the overflow occurs in a stack-allocated buffer due to insufficient bounds checking. This type of vulnerability allows attackers to manipulate program execution flow and potentially execute arbitrary code with the privileges of the cron daemon process. The attack vector is particularly concerning because cron jobs typically run with elevated privileges, making successful exploitation potentially catastrophic for system security.
The operational impact of CVE-1999-0768 extends beyond simple denial of service conditions to encompass potential system compromise and unauthorized access. When exploited successfully, this vulnerability could enable attackers to gain persistent access to systems through compromised cron jobs or by injecting malicious code into scheduled tasks. The vulnerability affects systems where cron is used for automated task scheduling, which is fundamental to most Unix-like operating systems including servers, workstations, and embedded devices. Attackers could leverage this weakness to establish backdoors, escalate privileges, or perform other malicious activities that would be difficult to detect or trace. The impact is particularly severe in enterprise environments where cron jobs often execute with root privileges, and where system administrators rely on automated processes for critical maintenance tasks.
Mitigation strategies for CVE-1999-0768 should focus on immediate patching of the affected Vixie Cron implementation on Red Hat systems, as well as implementing input validation measures for environment variables. System administrators should ensure that all cron jobs are updated to use patched versions of the cron daemon and that appropriate security updates are applied to the operating system. Additional defensive measures include restricting the use of environment variables in cron jobs, implementing proper input sanitization for MAILTO parameters, and monitoring cron job execution for unusual patterns or unauthorized modifications. Organizations should also consider implementing network segmentation and access controls to limit potential attack surfaces, while maintaining regular security audits of scheduled tasks and their associated privileges. The vulnerability highlights the importance of proper memory management and input validation in security-critical system components, aligning with ATT&CK technique T1053.003 for scheduled task/job hijacking and T1068 for local privilege escalation through vulnerable system services.