CVE-2006-1251 in sa-exim
Summary
by MITRE
Argument injection vulnerability in greylistclean.cron in sa-exim 4.2 allows remote attackers to delete arbitrary files via an email with a To field that contains a filename separated by whitespace, which is not quoted when greylistclean.cron provides the argument to the rm command.
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Analysis
by VulDB Data Team • 07/21/2018
The vulnerability described in CVE-2006-1251 represents a critical argument injection flaw within the sa-exim email system's greylistclean.cron component. This issue stems from improper handling of user-supplied input in a command execution context, specifically when processing email headers during the greylisting cleanup process. The vulnerability exists in the sa-exim 4.2 package where the greylistclean.cron script fails to properly quote or sanitize filename arguments extracted from email To fields before passing them to the rm command, creating a dangerous path for malicious exploitation.
The technical flaw manifests when an attacker crafts an email message with a specially formatted To field containing a filename that includes whitespace characters. When the greylistclean.cron script processes this email, it extracts the filename from the To header without proper quoting mechanisms and directly passes it as an argument to the rm command. This lack of input sanitization creates a classic command injection vulnerability where the shell interprets the whitespace-separated components as separate arguments, potentially allowing an attacker to execute arbitrary commands or delete unintended files from the system. The vulnerability is classified under CWE-78 as a failure to sanitize shell command arguments, making it a direct descendant of improper input validation patterns that have been consistently documented in security literature.
The operational impact of this vulnerability extends beyond simple file deletion capabilities, as it can be exploited to compromise the entire email server infrastructure. An attacker could leverage this vulnerability to remove critical system files, disable email services, or potentially escalate privileges within the system. The attack vector is particularly concerning because it requires only sending a specially crafted email to any user on the system, making it accessible to remote threat actors without requiring direct system access or authentication. This vulnerability directly maps to ATT&CK technique T1059.007 for Command and Scripting Interpreter: Unix Shell, as the exploitation involves the execution of shell commands through improper argument handling, and T1485 for Data Destruction, as the potential for arbitrary file deletion represents a significant data integrity threat.
Mitigation strategies for this vulnerability involve implementing proper input validation and argument sanitization within the greylistclean.cron script. System administrators should ensure that all user-supplied arguments passed to system commands are properly quoted and escaped to prevent shell interpretation of special characters. The recommended fix involves modifying the script to use proper shell escaping mechanisms or implementing a whitelist validation approach for filenames before they are passed to the rm command. Additionally, the system should be updated to a patched version of sa-exim that addresses this specific argument injection flaw, as the vulnerability represents a known weakness in the software's command execution handling. Organizations should also implement monitoring for unusual file deletion patterns and ensure that the cron job execution environment has appropriate access controls to limit potential damage from successful exploitation attempts.