CVE-2004-0423 in ssmtp
Summary
by MITRE
The log_event function in ssmtp 2.50.6 and earlier allows local users to overwrite arbitrary files via a symlink attack on the ssmtp.log temporary log file.
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Analysis
by VulDB Data Team • 06/18/2018
The vulnerability described in CVE-2004-0423 represents a critical file system security flaw within the ssmtp mail transfer agent version 2.50.6 and earlier. This issue stems from improper handling of temporary log files during the execution of the log_event function, creating a predictable race condition that adversaries can exploit through symbolic link attacks. The ssmtp utility, commonly used for sending email messages from command line applications, creates a temporary log file named ssmtp.log in a predictable location, which becomes vulnerable to manipulation by local users with minimal privileges.
The technical exploitation of this vulnerability occurs through a classic symlink attack pattern where a malicious local user creates a symbolic link with the name ssmtp.log in a location where the ssmtp utility will attempt to write to it. When the log_event function executes and attempts to write to what it believes is the legitimate log file, it actually writes to the target file specified by the symbolic link, allowing arbitrary file overwrite operations. This type of vulnerability falls under the category of CWE-377: Insecure Temporary File and CWE-378: Creation of Temporary File With Insecure Permissions, both of which are well-documented weaknesses in software security practices.
The operational impact of this vulnerability extends beyond simple file overwrites, as it provides attackers with the capability to modify critical system files, potentially leading to privilege escalation or persistent access to the compromised system. An attacker could leverage this vulnerability to overwrite configuration files, system binaries, or other sensitive data, depending on the permissions of the target files. This vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: Python, as it represents a path for executing malicious code through file system manipulation, and T1078 for Valid Accounts, since it requires only local user access to exploit. The vulnerability is particularly concerning in multi-user environments where local users might not have direct access to critical system files but can exploit this flaw to gain unauthorized access to system resources.
Mitigation strategies for this vulnerability should include immediate patching of ssmtp to versions that address the improper temporary file handling, implementing proper file permissions and ownership controls, and employing secure temporary file creation practices that prevent symbolic link attacks. System administrators should also consider implementing monitoring for suspicious file system activities and applying principle of least privilege concepts to limit the potential impact of such vulnerabilities. The vulnerability demonstrates the importance of proper temporary file handling practices and highlights the need for comprehensive security testing of software components that interact with the file system, particularly those that may be executed with elevated privileges or in multi-user environments.