CVE-2020-20253 in MikroTik
Summary
by MITRE • 05/18/2021
Mikrotik RouterOs before 6.47 (stable tree) suffers from a divison by zero vulnerability in the /nova/bin/lcdstat process. An authenticated remote attacker can cause a Denial of Service due to a divide by zero error.
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Analysis
by VulDB Data Team • 05/22/2021
The vulnerability identified as CVE-2020-20253 affects MikroTik RouterOS versions prior to 6.47 in the stable tree, presenting a critical division by zero flaw within the /nova/bin/lcdstat process. This issue represents a fundamental programming error that occurs when the system attempts to perform a mathematical operation involving division by zero, which is inherently undefined and causes system instability. The vulnerability specifically manifests in the lcdstat utility responsible for displaying system information on LCD displays, making it a component that interacts with hardware monitoring functions. The flaw exists in the software's handling of input parameters or system metrics that are processed by this utility, leading to a crash condition when the division operation encounters a zero denominator value.
The operational impact of this vulnerability extends beyond simple system instability as it creates a reliable denial of service condition that can be exploited by authenticated remote attackers. This means that an attacker who has gained access to the router's management interface can deliberately trigger the division by zero error through carefully crafted inputs or by manipulating system parameters that the lcdstat process monitors. The attack vector is particularly concerning because it requires only authentication credentials, making it accessible to individuals with legitimate administrative access or those who have compromised such credentials. The resulting system crash can interrupt network services, potentially leading to extended downtime for network infrastructure that relies on the affected router.
The technical nature of this vulnerability aligns with CWE-369, which specifically addresses the division by zero error condition that occurs when a program attempts to divide a number by zero, leading to a program crash or system instability. This classification indicates that the vulnerability stems from poor input validation or improper error handling within the lcdstat process, where the code does not adequately check for zero values before performing division operations. From an attack perspective, this vulnerability maps to the ATT&CK technique T1499.004 which involves network denial of service attacks through manipulation of network infrastructure components. The attack chain typically involves an authenticated user accessing the router's web interface or API, then executing commands that trigger the lcdstat utility with malicious parameters, ultimately causing the system to crash and become unavailable to legitimate users.
Mitigation strategies for CVE-2020-20253 primarily focus on immediate software updates to MikroTik RouterOS version 6.47 or later, which contains the necessary patches to address the division by zero condition. Organizations should also implement network monitoring to detect unusual patterns that might indicate exploitation attempts, particularly around authentication events and system resource utilization. Additionally, network administrators should consider implementing access controls that limit who can access the router's management interface, reducing the attack surface for potential exploitation. The vulnerability serves as a reminder of the critical importance of proper input validation and error handling in network infrastructure software, particularly in embedded systems where resource constraints might lead to inadequate defensive programming practices. Regular security assessments and vulnerability scanning of network infrastructure components remain essential for identifying similar issues before they can be exploited by malicious actors.