CVE-2021-1398 in IOS XE
Summary
by MITRE • 03/25/2021
A vulnerability in the boot logic of Cisco IOS XE Software could allow an authenticated, local attacker with level 15 privileges or an unauthenticated attacker with physical access to execute arbitrary code on the underlying Linux operating system of an affected device. This vulnerability is due to incorrect validations of specific function arguments that are passed to the boot script. An attacker could exploit this vulnerability by tampering with a specific file, which an affected device would process during the initial boot process. On systems that are protected by the Unified Extensible Firmware Interface (UEFI) secure boot feature, a successful exploit could allow the attacker to execute unsigned code at boot time and bypass the image verification check in the secure boot process of the affected device.
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Analysis
by VulDB Data Team • 04/04/2021
This vulnerability resides within the boot logic of Cisco IOS XE Software, representing a critical security flaw that undermines the integrity of the device's startup process. The vulnerability stems from insufficient validation mechanisms within the boot script's function argument processing, creating an exploitable condition that can be leveraged by attackers with varying privilege levels. The flaw specifically affects how the system handles certain file arguments during the initial boot sequence, allowing for malicious code execution at a fundamental system level. According to CWE-20, this represents a classic input validation error where the system fails to properly validate function arguments, creating a pathway for unauthorized code execution. The vulnerability's impact is particularly severe because it operates at the boot level, where the system has the highest privileges and the most direct access to underlying hardware resources.
The technical exploitation of this vulnerability requires either authenticated access with level 15 privileges or physical access to the device, providing attackers with multiple attack vectors. When an attacker successfully manipulates a specific file that the affected device processes during boot, the system executes arbitrary code on the underlying Linux operating system. This represents a privilege escalation scenario where the attacker gains elevated system privileges through the boot process, bypassing normal security controls. The exploitation mechanism leverages the trust placed in the boot script's argument validation, which should normally ensure that only legitimate system files are processed during startup. The vulnerability's design flaw allows for the execution of unsigned code, effectively undermining the security posture of devices that rely on UEFI secure boot mechanisms. This creates a particularly dangerous scenario where even systems with robust boot security measures can be compromised if the boot script fails to validate inputs properly.
The operational impact of this vulnerability extends beyond simple code execution, as it fundamentally compromises the device's security architecture and trust model. Attackers who successfully exploit this vulnerability can gain complete control over the affected device, potentially using it as a foothold for broader network attacks or as a pivot point for lateral movement within the network infrastructure. The ability to bypass UEFI secure boot verification represents a significant compromise of the device's security chain, as this feature is specifically designed to prevent unauthorized code execution during the boot process. Organizations using affected Cisco IOS XE devices face potential data breaches, service disruptions, and complete system compromise, particularly in environments where physical security is insufficient or where privileged accounts may be compromised. The vulnerability's impact is amplified by its potential for automated exploitation, as attackers can craft malicious boot files that will execute automatically during device restarts, making detection and remediation more challenging.
Mitigation strategies for this vulnerability must address both the immediate exploitation vectors and the underlying architectural flaws in the boot process validation. Cisco has released patches and software updates to address the specific argument validation issues within the boot script, requiring organizations to promptly apply these updates to affected systems. Network administrators should implement strict physical access controls to prevent unauthorized individuals from gaining the necessary access to exploit the vulnerability through physical means. The mitigation approach should also include monitoring for suspicious boot file modifications and implementing integrity checking mechanisms that can detect unauthorized changes to critical boot components. Organizations should consider implementing network segmentation and access controls that limit the potential impact of successful exploitation, particularly in environments where the vulnerability could be used as a stepping stone for broader network compromise. According to ATT&CK framework technique T1068, this vulnerability maps to the 'Exploitation for Privilege Escalation' tactic, where attackers leverage system weaknesses to gain elevated privileges. The remediation process must include thorough testing of patches in controlled environments before deployment to ensure that the updates do not introduce compatibility issues with existing network configurations or services.