CVE-2021-20133 in DIR-2640
Summary
by MITRE • 12/31/2021
Quagga Services on D-Link DIR-2640 less than or equal to version 1.11B02 are affected by an absolute path traversal vulnerability that allows a remote, authenticated attacker to set the "message of the day" banner to any file on the system, allowing them to read all or some of the contents of those files. Such sensitive information as hashed credentials, hardcoded plaintext passwords for other services, configuration files, and private keys can be disclosed in this fashion. Improper handling of filenames that identify virtual resources, such as "/dev/urandom" allows an attacker to effect a denial of service attack against the command line interfaces of the Quagga services (zebra and ripd).
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability CVE-2021-20133 represents a critical absolute path traversal flaw in the Quagga routing services running on D-Link DIR-2640 routers with firmware versions up to and including 1.11B02. This issue falls under CWE-22, which specifically addresses improper limitation of a pathname to a restricted directory, commonly known as path traversal attacks. The vulnerability exists within the handling of filenames used for setting the "message of the day" banner functionality, which is a legitimate administrative feature but becomes exploitable due to inadequate input validation and sanitization.
The technical exploitation of this vulnerability requires an attacker to be authenticated to the device, making it a privilege escalation issue rather than a purely remote attack vector. However, the impact remains severe as authenticated attackers can manipulate the system's banner setting functionality to read arbitrary files from the device's filesystem. This flaw allows access to sensitive information including hashed credentials stored in configuration files, plaintext passwords for other services that may be hardcoded within system files, and potentially private cryptographic keys. The vulnerability specifically leverages the improper handling of virtual device files such as "/dev/urandom" which should not be accessible through normal administrative interfaces, demonstrating a lack of proper resource access controls.
The operational impact of this vulnerability extends beyond mere information disclosure to include potential denial of service conditions affecting the Quagga services. When attackers exploit the path traversal to access command line interfaces through the zebra and ripd services, they can potentially disrupt routing operations and system availability. This creates a dual threat scenario where attackers can simultaneously extract sensitive data and compromise system integrity. The affected Quagga services are fundamental to network routing functionality, making this vulnerability particularly dangerous for network infrastructure devices. The attack surface is further expanded by the fact that these routers often serve as core network components in enterprise and home environments, potentially providing attackers with access to larger network segments.
Mitigation strategies for CVE-2021-20133 should prioritize firmware updates from D-Link to address the underlying path traversal implementation flaws. Network administrators should also implement strict access controls limiting administrative access to only authorized personnel and establish monitoring for unusual banner setting activities. The vulnerability demonstrates the importance of input validation in network service implementations and aligns with ATT&CK technique T1213 which covers data from information repositories. Organizations should also consider network segmentation to limit the potential impact of such vulnerabilities and implement regular security assessments of network infrastructure devices to identify similar path traversal issues in other vendor products. The flaw underscores the necessity of proper privilege separation and resource access controls in embedded systems where administrative interfaces may have overly permissive file access capabilities.