CVE-2018-16741 in Mgetty
Summary
by MITRE
An issue was discovered in mgetty before 1.2.1. In fax/faxq-helper.c, the function do_activate() does not properly sanitize shell metacharacters to prevent command injection. It is possible to use the ||, &&, or > characters within a file created by the "faxq-helper activate <jobid>" command.
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Analysis
by VulDB Data Team • 05/16/2023
The vulnerability identified as CVE-2018-16741 affects mgetty versions prior to 1.2.1 and represents a critical command injection flaw within the faxq-helper component. This issue resides in the fax/faxq-helper.c file where the do_activate() function fails to properly sanitize user input before incorporating it into shell commands. The vulnerability specifically manifests when processing file names containing shell metacharacters such as ||, &&, or > characters through the "faxq-helper activate <jobid>" command interface. The flaw stems from inadequate input validation and sanitization practices that allow malicious actors to inject arbitrary shell commands through crafted file names, potentially enabling full system compromise.
The technical implementation of this vulnerability follows a classic command injection pattern where user-controllable data flows directly into shell execution contexts without proper sanitization. When the faxq-helper component processes a job activation request, it accepts a job identifier that corresponds to a file name, but fails to validate or escape special shell characters that could alter command execution flow. The || operator allows command chaining where the second command executes if the first fails, the && operator ensures sequential execution only if the previous command succeeds, and the > operator enables output redirection to arbitrary files. These shell metacharacters can be strategically placed within file names to manipulate the underlying shell command execution, effectively bypassing normal security boundaries.
Operationally, this vulnerability presents significant risk to systems utilizing mgetty for fax processing, particularly in environments where fax services are accessible to untrusted users or where the faxq-helper component runs with elevated privileges. An attacker could exploit this weakness to execute arbitrary commands with the privileges of the faxq-helper process, potentially escalating to full system compromise. The attack surface extends to scenarios where fax job identifiers are derived from user input, such as in web interfaces or command line tools that interface with the fax system. The impact includes unauthorized data access, system command execution, privilege escalation, and potential persistence mechanisms that could allow continued unauthorized access to the compromised system.
Mitigation strategies for CVE-2018-16741 should focus on immediate patching of mgetty to version 1.2.1 or later where the sanitization issue has been addressed. System administrators should implement input validation measures that prevent special shell characters from being processed in file names or job identifiers. The principle of least privilege should be enforced by running faxq-helper processes with minimal required permissions and by implementing proper file name sanitization before any shell command execution. Network segmentation and access controls should limit exposure to this vulnerability by restricting access to fax services to authorized users only. Additionally, monitoring and logging should be enhanced to detect suspicious patterns in fax job processing that might indicate exploitation attempts. This vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and maps to ATT&CK technique T1059.001 for command and scripting interpreter, specifically shell scripting execution. Organizations should also consider implementing application whitelisting policies and regular security assessments to identify similar injection vulnerabilities in other system components.