CVE-1999-0769 in Cron
Summary
by MITRE
Vixie Cron on Linux systems allows local users to set parameters of sendmail commands via the MAILTO environmental variable.
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Analysis
by VulDB Data Team • 09/19/2024
The vulnerability described in CVE-1999-0769 represents a significant security flaw in the Vixie Cron implementation on Linux systems that enables local users to manipulate sendmail command parameters through the MAILTO environment variable. This issue stems from the improper handling of environment variables within the cron daemon's execution context, creating a potential vector for privilege escalation and command injection attacks. The vulnerability specifically affects systems where cron jobs are configured to send email notifications through sendmail, making it particularly relevant in environments where automated tasks generate output that needs to be emailed to system administrators or users.
The technical flaw manifests when cron executes scheduled tasks that involve sendmail commands, particularly when the MAILTO environment variable is set within the cron environment. This variable is typically used to specify the recipient of cron job output, but in vulnerable implementations, it can be manipulated to inject additional parameters or commands into the sendmail invocation. The vulnerability arises from the lack of proper input sanitization and environment variable handling within the cron daemon's execution flow, allowing malicious users to leverage this mechanism to execute arbitrary commands or modify sendmail behavior beyond normal operational parameters. This weakness creates a pathway for attackers to potentially escalate privileges or gain unauthorized access to system resources.
The operational impact of this vulnerability extends beyond simple command injection, as it can enable local users to manipulate system email delivery, potentially leading to information disclosure, denial of service, or privilege escalation. Attackers can exploit this vulnerability to send malicious emails, redirect system notifications, or even execute commands with elevated privileges if the cron environment has higher permissions than the attacking user. The vulnerability is particularly concerning in multi-user environments where users have access to cron scheduling capabilities but should not have the ability to modify system mail delivery parameters. This flaw can be leveraged to create persistent backdoors or to interfere with legitimate system administration tasks that rely on automated email notifications.
Mitigation strategies for CVE-1999-0769 should focus on implementing proper environment variable sanitization within cron implementations and restricting user access to potentially dangerous cron configurations. System administrators should ensure that cron jobs are properly configured with minimal required permissions and that environment variables are validated before being used in command execution. The implementation of secure coding practices, including input validation and environment variable handling, should be enforced in all cron daemon implementations. Additionally, organizations should consider implementing monitoring and alerting mechanisms to detect unusual cron job behavior or unauthorized modifications to mail delivery configurations. This vulnerability aligns with CWE-78 and CWE-79 categories related to command injection and input validation failures, and can be mapped to ATT&CK techniques involving privilege escalation and persistence through automated systems. Regular security audits and updates to cron implementations are essential to prevent exploitation of this and similar vulnerabilities in system administration tools.