CVE-2017-6796 in IOS XE
Summary
by MITRE
A vulnerability in the USB-modem code of Cisco IOS XE Software running on Cisco ASR 920 Series Aggregation Services Routers could allow an authenticated, local attacker to inject and execute arbitrary commands on the underlying operating system of an affected device. The vulnerability is due to improper input validation of the platform usb modem command in the CLI of the affected software. An attacker could exploit this vulnerability by modifying the platform usb modem command in the CLI of an affected device. A successful exploit could allow the attacker to inject and execute arbitrary commands on the underlying operating system of an affected device. Cisco Bug IDs: CSCve48949.
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Analysis
by VulDB Data Team • 01/11/2021
The vulnerability identified as CVE-2017-6796 represents a critical command injection flaw within Cisco IOS XE Software running on ASR 920 Series Aggregation Services Routers. This security weakness stems from inadequate input validation mechanisms within the platform usb modem command implementation in the command line interface. The vulnerability specifically targets the authentication and authorization controls that govern access to the router's underlying operating system through the CLI interface. An authenticated local attacker with sufficient privileges can exploit this flaw to manipulate the command execution flow and gain unauthorized access to the system's core operating environment. The issue manifests when the attacker modifies the platform usb modem command through the CLI, effectively bypassing normal security controls and executing malicious code directly on the router's operating system. This represents a significant elevation of privileges from a standard user account to system-level access, enabling attackers to perform actions that could compromise the entire network infrastructure.
The technical exploitation of this vulnerability falls under the Common Weakness Enumeration category of CWE-77 and CWE-94, which respectively address command injection and code injection flaws. The attack vector leverages the principle of insufficient input validation, where the CLI interface fails to properly sanitize user inputs before processing them through the underlying operating system commands. The vulnerability operates at the command execution layer within the router's software stack, allowing attackers to inject malicious command sequences that are then interpreted and executed by the system shell. This type of vulnerability is particularly dangerous in network infrastructure devices because it provides direct access to the operating system kernel and system-level processes. The exploitation requires local authentication, meaning the attacker must already possess valid credentials to access the router's CLI, but once achieved, the privilege escalation is complete. The vulnerability demonstrates a failure in the principle of least privilege enforcement, where the system does not adequately validate or restrict command inputs that could lead to arbitrary code execution.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential network disruption, data compromise, and unauthorized access to sensitive network infrastructure. An attacker who successfully exploits this vulnerability could potentially gain complete control over the router's operations, including the ability to modify routing tables, intercept network traffic, disable security features, or establish persistent access points within the network. The affected Cisco ASR 920 Series routers serve as critical aggregation points in many network architectures, making this vulnerability particularly dangerous as it could allow attackers to compromise entire network segments. The vulnerability also poses risks to network monitoring and logging capabilities since the attacker could modify or disable system logging functions to avoid detection. Additionally, the exploitation could lead to denial of service conditions by corrupting system processes or consuming excessive system resources. The presence of this vulnerability in widely deployed network infrastructure devices means that successful exploitation could have cascading effects throughout connected networks, potentially enabling further attacks against downstream systems.
Organizations should implement immediate mitigation strategies including applying the relevant Cisco security patches and updates released to address this vulnerability. The recommended approach involves upgrading to Cisco IOS XE Software versions that contain the necessary input validation fixes for the platform usb modem command. Network administrators should also implement strict access controls and monitor CLI access logs for any suspicious command sequences or unauthorized access attempts. The principle of defense in depth should be applied by segmenting network access and implementing additional authentication layers beyond simple CLI access. Configuration management practices should include regular review of router configurations and enforcement of secure baseline configurations that minimize the attack surface. Network monitoring solutions should be enhanced to detect anomalous command execution patterns that could indicate exploitation attempts. Additionally, implementing network access control lists and firewall rules to restrict access to router management interfaces can help limit the potential impact of this vulnerability. The vulnerability highlights the importance of maintaining current security patches and conducting regular vulnerability assessments of critical network infrastructure components to prevent exploitation of known security flaws.