CVE-2018-16743 in Mgetty
Summary
by MITRE
An issue was discovered in mgetty before 1.2.1. In contrib/next-login/login.c, the command-line parameter username is passed unsanitized to strcpy(), which can cause a stack-based buffer overflow.
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Analysis
by VulDB Data Team • 03/23/2020
The vulnerability identified as CVE-2018-16743 represents a critical stack-based buffer overflow flaw in the mgetty package version 1.2.0 and earlier. This issue resides within the command-line argument processing mechanism of the login utility component, specifically in the contrib/next-login/login.c source file where user-provided username parameters are directly passed to the strcpy() function without proper input validation or sanitization. The mgetty package serves as aGetty implementation for serial line login sessions and is commonly deployed in embedded systems and legacy environments where serial console access is required for system administration and maintenance purposes. The flaw manifests when an attacker provides a specially crafted username argument that exceeds the predetermined buffer size allocated for username storage, thereby overwriting adjacent memory locations on the stack.
The technical exploitation of this vulnerability follows a classic buffer overflow pattern that violates fundamental security principles of input validation and memory management. When the strcpy() function receives an unsanitized username parameter, it copies the entire string content to a fixed-size buffer without checking the source length against the destination buffer capacity. This behavior creates a predictable memory corruption scenario where attacker-controlled data can overwrite stack canaries, return addresses, and other critical program state information. The vulnerability directly maps to CWE-121, Stack-based Buffer Overflow, and CWE-787, Out-of-bounds Write, both of which are categorized under the broader weakness of improper input validation. The attack vector is particularly concerning because it requires only command-line argument manipulation, making exploitation accessible through normal program invocation interfaces.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions to potentially enable arbitrary code execution on affected systems. An attacker who successfully exploits this buffer overflow could manipulate the program flow by overwriting return addresses and executing malicious code within the context of the mgetty process. This privilege escalation scenario is particularly dangerous in environments where mgetty operates with elevated privileges or where the serial console access is used for system administration tasks. The vulnerability affects systems where mgetty is deployed for serial line authentication, including embedded devices, industrial control systems, and legacy server environments that rely on serial console access for remote management. Given that the affected version predates proper input sanitization measures, any system running mgetty 1.2.0 or earlier is potentially vulnerable to remote exploitation through carefully crafted username arguments.
Mitigation strategies for CVE-2018-16743 should prioritize immediate software updates to mgetty version 1.2.1 or later, which incorporates proper input validation and buffer size checking mechanisms. System administrators should implement input sanitization measures at the application level by replacing unsafe strcpy() calls with safer alternatives such as strlcpy() or by implementing explicit length checks before string copying operations. Network-level protections can include restricting access to serial console interfaces and implementing proper authentication mechanisms to limit exposure of vulnerable login interfaces. The vulnerability demonstrates the importance of adhering to secure coding practices as outlined in the software security development lifecycle and aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter, particularly when considering the potential for command execution through compromised login processes. Organizations should conduct comprehensive vulnerability assessments to identify all systems running vulnerable versions of mgetty and establish monitoring procedures to detect potential exploitation attempts targeting this specific buffer overflow vulnerability.