CVE-2020-3404 in IOS XE
Summary
by MITRE
A vulnerability in the persistent Telnet/Secure Shell (SSH) CLI of Cisco IOS XE Software could allow an authenticated, local attacker to gain shell access on an affected device and execute commands on the underlying operating system (OS) with root privileges. The vulnerability is due to insufficient enforcement of the consent token in authorizing shell access. An attacker could exploit this vulnerability by authenticating to the persistent Telnet/SSH CLI on an affected device and requesting shell access. A successful exploit could allow the attacker to gain shell access on the affected device and execute commands on the underlying OS with root privileges.
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Analysis
by VulDB Data Team • 09/25/2020
The vulnerability identified as CVE-2020-3404 resides within the persistent Telnet/Secure Shell CLI implementation of Cisco IOS XE Software, representing a critical security flaw that undermines the integrity of device access controls. This issue specifically targets the authorization mechanisms that govern shell access privileges, creating a pathway for authenticated local attackers to escalate their privileges from standard user level to root access on affected network devices. The vulnerability stems from inadequate enforcement of consent tokens during the shell access authorization process, effectively bypassing the security controls that should prevent unauthorized privilege escalation. Cisco IOS XE Software serves as the foundation for numerous enterprise networking devices including routers and switches, making this vulnerability particularly concerning given the widespread deployment of these systems across corporate and government networks. The flaw manifests when an authenticated user attempts to request shell access through the persistent CLI interface, exploiting a weakness in the token validation process that should otherwise prevent such privilege escalation.
The technical exploitation of CVE-2020-3404 involves a sophisticated attack vector that leverages the existing authentication state of a legitimate user to gain elevated privileges. When an attacker successfully authenticates to the persistent Telnet or SSH CLI interface, the system should enforce strict authorization controls to prevent shell access requests from being granted without proper verification. However, the insufficient enforcement of consent tokens means that the system fails to properly validate the authorization context, allowing the attacker to request and receive shell access that grants root privileges on the underlying operating system. This vulnerability directly maps to CWE-284, which addresses improper access control mechanisms, and represents a classic case of privilege escalation through inadequate authorization checks. The flaw demonstrates a fundamental breakdown in the principle of least privilege, where the system fails to properly enforce the boundaries between standard user access and administrative shell access. Attackers can exploit this vulnerability to execute arbitrary commands with the highest possible privileges, potentially compromising the entire network infrastructure controlled by the affected device.
The operational impact of CVE-2020-3404 extends far beyond simple privilege escalation, as it provides attackers with complete control over affected network devices and their underlying operating systems. Once an attacker gains root access through this vulnerability, they can modify device configurations, install malicious software, monitor network traffic, and potentially use the compromised device as a pivot point to attack other systems within the network. The persistent nature of the Telnet/SSH CLI interface means that the vulnerability remains exploitable for as long as the service remains active, providing attackers with sustained access to the compromised device. This threat is particularly severe in enterprise environments where network devices often serve as critical infrastructure components, and where the compromise of a single device can lead to widespread network disruption or data breaches. The vulnerability affects multiple Cisco IOS XE Software versions, making it a widespread concern that impacts numerous network deployments across different organizations. The potential for lateral movement within networks increases significantly when attackers can execute commands with root privileges on network infrastructure devices, as these systems often have access to sensitive network segments and critical data resources.
Mitigation strategies for CVE-2020-3404 should focus on immediate patching of affected Cisco IOS XE Software versions, as Cisco has released security updates to address this vulnerability. Organizations should prioritize patch management efforts to ensure all affected devices receive the necessary security fixes promptly. Network segmentation and access control measures can provide additional layers of defense by limiting the scope of potential exploitation and reducing the attack surface for authenticated users. Implementing strict monitoring and logging of shell access requests can help detect unauthorized privilege escalation attempts, while disabling unnecessary Telnet services in favor of more secure SSH implementations reduces the available attack vectors. The vulnerability highlights the importance of proper authorization token enforcement in network device security architectures and demonstrates the critical need for robust access control mechanisms in enterprise networking infrastructure. Organizations should also consider implementing network access control policies that restrict shell access to only essential administrative personnel and require multi-factor authentication for elevated privilege access. Regular security audits and vulnerability assessments should be conducted to identify similar authorization flaws in other network components and ensure comprehensive protection against privilege escalation attacks.