CVE-2017-6773 in StarOS
Summary
by MITRE
A vulnerability in the CLI of Cisco ASR 5000 Series Aggregated Services Routers running the Cisco StarOS operating system could allow an authenticated, local attacker to bypass the CLI restrictions and execute commands on the underlying operating system. The vulnerability is due to insufficient input sanitization of user-supplied input at the CLI. An attacker could exploit this vulnerability by crafting a script on the device that will allow them to bypass built-in restrictions. An exploit could allow the unauthorized user to launch the CLI directly from a command shell. Cisco Bug IDs: CSCvd47722. Known Affected Releases: 21.0.v0.65839.
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Analysis
by VulDB Data Team • 01/09/2021
The vulnerability identified as CVE-2017-6773 affects Cisco ASR 5000 Series Aggregated Services Routers operating on the Cisco StarOS platform, representing a critical local privilege escalation flaw that undermines the security posture of these network infrastructure devices. This vulnerability specifically targets the Command Line Interface implementation where insufficient input sanitization creates exploitable conditions for authenticated local attackers to bypass established security controls. The flaw exists within the CLI subsystem of the StarOS operating system, which is designed to provide administrative access to router functions while maintaining strict security boundaries between different privilege levels. The vulnerability's impact extends beyond simple command execution as it allows attackers to effectively circumvent the intended security model that separates standard user access from privileged administrative functions.
The technical root cause of this vulnerability stems from inadequate input validation mechanisms within the CLI parser implementation, which fails to properly sanitize or filter user-supplied input before processing commands. This weakness enables attackers to craft malicious input sequences that can manipulate the CLI behavior to execute arbitrary operating system commands directly from the underlying Linux environment. The vulnerability is particularly dangerous because it requires only local authentication credentials, meaning that any user with legitimate access to the device can potentially exploit this flaw. Attackers can leverage this vulnerability by creating specially crafted scripts or command sequences that bypass the CLI's built-in restriction mechanisms, effectively allowing them to escalate privileges and gain direct access to the underlying operating system shell. The exploitation process involves understanding the CLI's internal parsing logic and identifying specific input patterns that trigger the sanitization bypass.
From an operational perspective, this vulnerability presents a significant risk to network security infrastructure as it allows attackers to gain unauthorized access to the underlying operating system while maintaining the appearance of legitimate administrative activity. The impact extends to potential data exfiltration, system modification, and further network reconnaissance activities that could compromise the entire network infrastructure. The vulnerability's exploitation does not require external network access or complex attack vectors, making it particularly dangerous as it can be leveraged by insiders or attackers who have already gained local access to the device. The affected releases including version 21.0.v0.65839 indicate that this flaw existed for a considerable period, potentially allowing attackers to establish persistent access and conduct long-term reconnaissance activities without detection. The Cisco Bug ID CSCvd47722 documents the specific implementation details and provides guidance for remediation efforts.
Organizations should implement immediate mitigations including applying the latest security patches provided by Cisco to address this vulnerability. Network administrators should also conduct thorough access reviews to ensure that only authorized personnel have local access to these devices, implementing least privilege principles and monitoring access logs for suspicious activities. The vulnerability aligns with CWE-20, which describes improper input validation, and can be categorized under ATT&CK technique T1059 for command and scripting interpreter, as it allows for arbitrary command execution. Additionally, this vulnerability demonstrates characteristics of privilege escalation attacks and can be classified under ATT&CK technique T1068, which addresses local privilege escalation. Security monitoring should focus on detecting unusual command execution patterns and unauthorized access attempts to the CLI interface. The implementation of network segmentation and access controls around these critical devices can provide additional defense-in-depth layers to protect against potential exploitation of this vulnerability.