CVE-2020-3455 in FXOS
Summary
by MITRE • 10/22/2020
A vulnerability in the secure boot process of Cisco FXOS Software could allow an authenticated, local attacker to bypass the secure boot mechanisms. The vulnerability is due to insufficient protections of the secure boot process. An attacker could exploit this vulnerability by injecting code into a specific file that is then referenced during the device boot process. A successful exploit could allow the attacker to break the chain of trust and inject code into the boot process of the device which would be executed at each boot and maintain persistence across reboots.
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Analysis
by VulDB Data Team • 11/25/2020
The vulnerability identified as CVE-2020-3455 resides within the secure boot implementation of Cisco FXOS Software, representing a critical weakness in the device's integrity protection mechanisms. This flaw specifically targets the chain of trust that ensures only authorized and verified code executes during the boot process. The vulnerability stems from inadequate safeguards that should normally prevent unauthorized modifications to critical boot components, creating an exploitable pathway for malicious actors who possess local authentication credentials. The secure boot process, which is fundamental to preventing rootkit installations and maintaining system integrity, becomes compromised when attackers can manipulate specific files that are loaded during device initialization. This represents a significant departure from the expected security posture where boot processes should remain impervious to tampering by unauthorized parties.
The technical exploitation of this vulnerability requires an authenticated local attacker who can modify specific files within the device's filesystem that are referenced during the boot sequence. The flaw manifests as insufficient validation mechanisms that fail to properly verify the integrity of files that are critical to the boot process, particularly those involved in the digital signature verification and code execution phases. Attackers can inject malicious code into designated files that are loaded during startup, effectively creating a persistent backdoor that survives device reboots. This exploitation technique leverages the trust relationship between boot components and the operating system, allowing the attacker to break the chain of trust established by the secure boot implementation. The vulnerability is classified under CWE-327, which deals with broken or weak cryptographic implementations, as the secure boot process fails to properly enforce cryptographic verification of boot components.
The operational impact of CVE-2020-3455 extends beyond simple unauthorized code execution, as it enables persistent threat actor presence on affected Cisco devices. Once successfully exploited, the malicious code becomes part of the boot process and executes automatically at each device restart, providing attackers with long-term access and control. This persistence mechanism is particularly concerning as it bypasses traditional endpoint detection and response measures that typically focus on runtime activities rather than boot-time modifications. The vulnerability affects Cisco Firepower appliances and other devices running FXOS Software, potentially compromising network security infrastructure and enabling attackers to maintain access even after system maintenance or updates. This represents a significant threat to network security operations, as it allows adversaries to establish stealthy footholds that can evade detection by conventional security monitoring tools.
Mitigation strategies for CVE-2020-3455 should prioritize immediate patch deployment from Cisco, as the vulnerability requires no specialized knowledge or tools beyond legitimate administrative access to exploit. Organizations must ensure comprehensive network device inventory management to identify all affected systems running vulnerable FXOS versions, particularly those that are part of critical network infrastructure. The remediation process involves applying Cisco's official security patches that strengthen the secure boot implementation and improve file integrity verification mechanisms. Network administrators should also implement enhanced monitoring of boot processes and file system changes, utilizing security information and event management systems to detect unauthorized modifications to critical boot components. Additionally, privileged access controls should be strictly enforced, limiting local authentication access to only authorized personnel and implementing multi-factor authentication where possible. This vulnerability aligns with ATT&CK technique T1542.001, which covers the use of boot or logon initialization scripts, and represents a critical threat to system integrity that requires immediate attention from security operations teams responsible for maintaining network infrastructure security.