CVE-2021-1145 in StarOS
Summary
by MITRE • 01/14/2021
A vulnerability in the Secure FTP (SFTP) of Cisco StarOS for Cisco ASR 5000 Series Routers could allow an authenticated, remote attacker to read arbitrary files on an affected device. To exploit this vulnerability, the attacker would need to have valid credentials on the affected device. The vulnerability is due to insecure handling of symbolic links. An attacker could exploit this vulnerability by sending a crafted SFTP command to an affected device. A successful exploit could allow the attacker to read arbitrary files on the affected device.
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Analysis
by VulDB Data Team • 02/13/2021
This vulnerability exists within the Secure FTP implementation of Cisco StarOS operating system on Cisco ASR 5000 Series Routers, representing a critical security flaw that could enable authenticated remote attackers to access sensitive system files. The vulnerability stems from improper handling of symbolic links during SFTP operations, creating a path traversal condition that allows attackers to bypass normal file access controls. The flaw specifically affects the SFTP subsystem's processing of symbolic link references, where the system fails to properly validate or sanitize symbolic link paths before resolving them to actual file locations. This insecure handling of symbolic links creates a direct pathway for attackers to access files outside of their intended scope, potentially exposing system configuration files, authentication credentials, or other sensitive data stored on the device.
The exploitation of this vulnerability requires an attacker to possess valid authentication credentials for the affected device, establishing a privileged execution context before attempting the attack. This authentication requirement provides some defense-in-depth but does not eliminate the risk entirely, as the vulnerability can be leveraged by malicious insiders or compromised accounts. The attack vector involves sending specifically crafted SFTP commands that manipulate symbolic link references to traverse the filesystem hierarchy and access arbitrary files. According to the CWE catalog, this vulnerability maps to CWE-22 Path Traversal, which describes the condition where untrusted input is used to construct file paths without proper validation, leading to unauthorized file access. The attack technique aligns with ATT&CK tactic TA0005 Defense Evasion and technique T1059 Command and Scripting Interpreter, as the attacker can execute commands through the SFTP interface to manipulate file access patterns.
The operational impact of this vulnerability extends beyond simple unauthorized file access, as it could potentially enable attackers to extract sensitive information that could be used for further exploitation or to compromise the overall security posture of the network infrastructure. The affected Cisco ASR 5000 Series Routers serve as critical components in telecommunications networks, making the potential compromise of these devices particularly concerning for network security. Attackers could potentially access system configuration files that contain sensitive information such as encryption keys, user credentials, or network topology details that could facilitate more sophisticated attacks. The vulnerability's impact is amplified by the fact that the affected devices typically operate in environments where they handle sensitive customer data or network control information, making the potential data exposure significant for organizations relying on these platforms. Organizations should prioritize immediate remediation through official Cisco security advisories and patches while implementing network segmentation and access control measures to limit the potential impact of credential compromise.
This vulnerability demonstrates the importance of proper input validation and secure file system operations in network infrastructure devices. The insecure handling of symbolic links represents a common pattern in software development where developers may not adequately consider the security implications of file system operations involving symbolic references. The vulnerability highlights the need for comprehensive security testing of network infrastructure components, particularly those handling user authentication and file access operations. Organizations should implement monitoring solutions to detect unusual SFTP activity patterns and establish robust access control policies that limit user privileges to only necessary system resources. The incident underscores the critical nature of maintaining current security patches and following vendor security advisories, as the vulnerability could be exploited by attackers with minimal technical expertise once they obtain valid credentials. Security teams should also consider implementing additional logging and audit capabilities for SFTP operations to detect and respond to potential exploitation attempts.