CVE-2004-0156 in ssmtp
Summary
by MITRE
Format string vulnerabilities in the (1) die or (2) log_event functions for ssmtp before 2.50.6 allow remote mail relays to cause a denial of service and possibly execute arbitrary code.
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Analysis
by VulDB Data Team • 07/19/2019
The vulnerability identified as CVE-2004-0156 represents a critical format string flaw within the ssmtp mail transfer agent version 2.50.5 and earlier. This issue affects two core functions: die and log_event, which are fundamental components responsible for error handling and logging operations within the mail relay system. The ssmtp utility serves as a simple mail transfer agent that forwards mail to a configured relay host, making it a critical component in many email delivery chains. The vulnerability arises from improper handling of user-supplied input within format string operations, creating an exploitable condition that can be leveraged by remote attackers to manipulate the program's execution flow.
Format string vulnerabilities occur when a program uses user input directly in format string functions such as printf, sprintf, or fprintf without proper validation or sanitization. In this case, the die and log_event functions in ssmtp fail to properly escape or validate input parameters before incorporating them into format string operations. When an attacker can control the input to these functions, they can inject format specifiers that cause the program to read from or write to arbitrary memory locations. This fundamental flaw allows for both denial of service conditions through stack corruption and potential code execution through carefully crafted input that can overwrite function pointers or return addresses.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable remote code execution on systems running vulnerable versions of ssmtp. Remote mail relays can exploit this weakness by sending specially crafted email messages that trigger the vulnerable functions with malicious format strings. The consequences include complete system compromise, data theft, or persistent backdoor access through code execution, making this vulnerability particularly dangerous in environments where ssmtp is used as a mail relay. The vulnerability's severity is amplified by the fact that it affects the core logging and error handling mechanisms, meaning that any email traffic could potentially trigger the exploit.
Mitigation strategies for CVE-2004-0156 primarily involve upgrading to ssmtp version 2.50.6 or later, which contains patches addressing the format string vulnerabilities in both die and log_event functions. System administrators should also implement network-level restrictions to limit mail relay access and monitor for unusual email traffic patterns that might indicate exploitation attempts. Additional protective measures include disabling unnecessary mail relay functionality, implementing proper input validation at network boundaries, and conducting regular security assessments of mail infrastructure components. This vulnerability aligns with CWE-134, which specifically addresses format string vulnerabilities in software applications, and corresponds to techniques described in the ATT&CK framework under privilege escalation and remote code execution tactics. Organizations should prioritize immediate remediation of this vulnerability due to its potential for remote code execution and the availability of patched versions that address the underlying format string handling issues.