CVE-2018-16744 in Mgetty
Summary
by MITRE
An issue was discovered in mgetty before 1.2.1. In fax_notify_mail() in faxrec.c, the mail_to parameter is not sanitized. It could allow for command injection if untrusted input can reach it, because popen is used.
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Analysis
by VulDB Data Team • 03/23/2020
The vulnerability identified as CVE-2018-16744 represents a critical command injection flaw in the mgetty package version 1.2.0 and earlier. This issue resides within the fax_notify_mail() function located in the faxrec.c source file, where the mail_to parameter undergoes insufficient input validation and sanitization. The vulnerability stems from the improper handling of user-supplied data that flows directly into system calls without adequate protection mechanisms, creating a pathway for malicious actors to execute arbitrary commands on the affected system. The flaw specifically manifests when the popen function is employed to process the unsanitized mail_to parameter, which allows attackers to inject shell commands that will be executed with the privileges of the mgetty process.
This vulnerability falls under the CWE-78 category of Improper Neutralization of Special Elements used in an OS Command, which is a well-documented weakness in software systems where user input is directly incorporated into operating system commands without proper sanitization. The attack vector typically involves an attacker sending a fax with a maliciously crafted recipient address that contains shell command injection payloads. When mgetty processes this fax notification and attempts to send an email to the specified address, the unsanitized input is passed directly to the popen function, enabling arbitrary command execution. The operational impact extends beyond simple command injection as it can lead to full system compromise, privilege escalation, and potential lateral movement within network environments where mgetty is deployed.
The security implications of this vulnerability are particularly severe in environments where mgetty serves as a fax gateway or receives untrusted fax inputs from external sources. The attack surface is broad as any system running mgetty version 1.2.0 or earlier that accepts fax communications could be vulnerable to exploitation. The ATT&CK framework categorizes this vulnerability under the T1059.001 technique for Command and Scripting Interpreter, specifically shell commands, as the exploitation relies on the execution of shell commands through the vulnerable popen function. This allows attackers to potentially gain unauthorized access to system resources, escalate privileges, and establish persistent access points. The vulnerability also aligns with T1078.004 for Valid Accounts, as successful exploitation could provide attackers with legitimate system access through the mgetty service account.
Mitigation strategies for CVE-2018-16744 primarily focus on immediate remediation through updating to mgetty version 1.2.1 or later, which includes proper input sanitization and validation mechanisms. Organizations should also implement network segmentation to limit exposure of mgetty services to untrusted networks and establish strict input validation policies for all fax-related communications. Additional protective measures include monitoring fax traffic for suspicious patterns, implementing proper access controls for fax services, and conducting regular security assessments of fax gateway systems. The vulnerability demonstrates the critical importance of input validation and the principle of least privilege in system design, as proper sanitization of user inputs before system command execution could have prevented this security flaw. System administrators should also consider implementing intrusion detection systems to monitor for potential exploitation attempts and maintain updated threat intelligence on similar command injection vulnerabilities in fax and telephony systems.