CVE-2020-15001 in YubiKey
Summary
by MITRE
An information leak was discovered on Yubico YubiKey 5 NFC devices 5.0.0 to 5.2.6 and 5.3.0 to 5.3.1. The OTP application allows a user to set optional access codes on OTP slots. This access code is intended to prevent unauthorized changes to OTP configurations. The access code is not checked when updating NFC specific components of the OTP configurations. This may allow an attacker to access configured OTPs and passwords stored in slots that were not configured by the user to be read over NFC, despite a user having set an access code. (Users who have not set an access code, or who have not configured the OTP slots, are not impacted by this issue.)
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Analysis
by VulDB Data Team • 10/29/2020
The vulnerability CVE-2020-15001 represents a critical information disclosure flaw in Yubico YubiKey 5 NFC devices running firmware versions 5.0.0 through 5.2.6 and 5.3.0 through 5.3.1. This weakness specifically affects the OTP (One-Time Password) application functionality where users can establish optional access codes to protect OTP slot configurations. The security mechanism intended to prevent unauthorized modifications to these slots fails to properly validate access codes when updating NFC-specific components of the OTP configurations. This design flaw creates a significant bypass opportunity that allows attackers to access sensitive OTPs and passwords stored in slots that were not explicitly configured for NFC reading, despite the presence of access codes that should have restricted such access.
The technical implementation of this vulnerability stems from inconsistent validation logic within the YubiKey's firmware where access code checks are properly enforced for most configuration updates but are omitted during the specific process of updating NFC-related parameters. This creates a gap in the security model where the authentication mechanism that should protect sensitive data becomes ineffective for NFC operations. The flaw operates at the application layer within the OTP application, specifically affecting how the device handles access code validation during different types of configuration updates. According to CWE classification, this vulnerability aligns with CWE-284 Access Control Bypass, as it allows unauthorized access to protected resources through a failure in access control enforcement. The issue represents a classic case of incomplete input validation and access control implementation where the system fails to consistently apply security checks across all operational paths.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable credential theft and unauthorized access to systems protected by OTP-based authentication. Attackers who can perform NFC-based interactions with affected YubiKey devices can extract sensitive information from OTP slots that should have been protected by access codes, effectively neutralizing the security provided by these protective measures. This weakness particularly affects scenarios where users have configured access codes but also have NFC-enabled slots that were not properly secured against unauthorized reading. The vulnerability affects users who have configured access codes but not properly understood the security implications of NFC operations, creating a false sense of security. From an ATT&CK perspective, this vulnerability maps to T1552.001 Unsecured Credentials and T1078 Valid Accounts, as it enables attackers to potentially obtain valid authentication tokens that should have been protected by access controls.
Mitigation strategies for this vulnerability require immediate firmware updates to affected YubiKey devices, as Yubico has released patches addressing the specific access control bypass. Users should disable NFC functionality on devices where it is not required, particularly in environments where physical security cannot be guaranteed. Security administrators should conduct comprehensive inventory assessments to identify all affected devices and implement monitoring for unauthorized NFC interactions. The recommended approach includes disabling NFC capabilities entirely if not needed, as the vulnerability affects the core security model of the device. Organizations should also implement additional authentication layers and regularly audit their OTP configurations to ensure that access codes are properly enforced across all operational modes. Network administrators should consider implementing device-specific policies that restrict NFC operations in sensitive environments and establish procedures for immediate device replacement when vulnerabilities are identified. The fundamental requirement for mitigation involves ensuring that all device firmware versions are current with security patches that address the inconsistent access control validation during NFC operations.