CVE-2020-3416 in IOS XE
Summary
by MITRE
Multiple vulnerabilities in the initialization routines that are executed during bootup of Cisco IOS XE Software for Cisco ASR 900 Series Aggregation Services Routers with a Route Switch Processor 3 (RSP3) installed could allow an authenticated, local attacker with high privileges to execute persistent code at bootup and break the chain of trust. These vulnerabilities are due to incorrect validations by boot scripts when specific ROM monitor (ROMMON) variables are set. An attacker could exploit these vulnerabilities by copying a specific file to the local file system of an affected device and defining specific ROMMON variables. A successful exploit could allow the attacker to run arbitrary code on the underlying operating system (OS) with root privileges. To exploit these vulnerabilities, an attacker would need to have access to the root shell on the device or have physical access to the device.
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Analysis
by VulDB Data Team • 09/25/2020
The vulnerability identified as CVE-2020-3416 represents a critical security flaw in Cisco IOS XE Software running on Cisco ASR 900 Series Aggregation Services Routers equipped with Route Switch Processor 3 hardware. This issue stems from inadequate validation mechanisms within the boot initialization routines that are executed during device startup processes. The flaw specifically affects the ROM monitor (ROMMON) environment where certain variables are processed during bootup, creating a persistent code execution vector that can compromise the device's integrity and security posture. The vulnerability is particularly concerning because it enables attackers to establish persistent access during the boot process, effectively bypassing normal security controls that would typically be active once the system is fully operational. This type of attack vector directly undermines the fundamental security principles of trust establishment and code integrity verification that are essential for network infrastructure devices.
The technical exploitation of CVE-2020-3416 relies on the manipulation of ROMMON variables through specific boot scripts that fail to properly validate input parameters. When an attacker successfully sets these variables and copies a malicious file to the local file system, the device's boot process executes arbitrary code with root privileges, effectively granting complete control over the underlying operating system. The vulnerability demonstrates a classic case of insufficient input validation and privilege escalation, where the system fails to properly authenticate or verify the legitimacy of boot-time configurations. This flaw aligns with CWE-20, which addresses "Improper Input Validation," and CWE-78, which covers "Improper Neutralization of Special Elements used in OS Command Injection." The attack requires either physical access to the device or root shell access, but once achieved, the attacker can establish persistent backdoors that survive system reboots, making the compromise particularly dangerous for network infrastructure security.
The operational impact of this vulnerability extends beyond simple code execution, as it fundamentally compromises the chain of trust that is critical for network security infrastructure. Network administrators face the risk of complete device compromise, which could lead to unauthorized network access, data exfiltration, or disruption of critical network services. The persistent nature of the exploit means that even if administrators attempt to reboot the device or apply security patches, the malicious code will re-execute during bootup, maintaining the attacker's presence. This vulnerability particularly affects enterprise and service provider networks where ASR 900 Series routers serve as critical aggregation points, potentially allowing attackers to pivot to other network segments or establish long-term surveillance capabilities. The attack vector's requirement for either physical access or root shell access means that organizations must also strengthen their physical security measures and implement strict access controls to prevent unauthorized individuals from gaining the necessary privileges to exploit this vulnerability.
Organizations should implement multiple layers of defense to mitigate the risks associated with CVE-2020-3416, including immediate deployment of Cisco's official security patches and updates. Network segmentation strategies should be employed to limit the potential impact of a successful compromise, while strict access controls and privilege management should be enforced to prevent unauthorized access to root shells or physical device access. Monitoring systems should be configured to detect unusual boot patterns or file system modifications that could indicate exploitation attempts, and regular security audits should verify the integrity of boot processes and ROMMON configurations. The vulnerability also highlights the importance of implementing the principle of least privilege and maintaining comprehensive network access control policies. Organizations should also consider implementing network-based intrusion detection systems that can identify suspicious activities related to boot processes and file system modifications, as well as establishing incident response procedures specifically designed to address persistent boot-time compromises. This vulnerability demonstrates the critical need for robust firmware security practices and continuous monitoring of network infrastructure components to prevent exploitation of low-level system vulnerabilities that could lead to complete system compromise.