CVE-2016-10398 in Android
Summary
by MITRE
Android 6.0 has an authentication bypass for attackers with root and physical access. Cryptographic authentication tokens (AuthTokens) used by the Trusted Execution Environment (TEE) are protected by a weak challenge. This allows adversaries to replay previously captured responses and use the TEE without authenticating. All apps using authentication-gated cryptography are vulnerable to this attack, which was confirmed on the LG Nexus 5X.
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Analysis
by VulDB Data Team • 10/25/2019
The vulnerability described in CVE-2016-10398 represents a critical security flaw in Android 6.0's implementation of the Trusted Execution Environment architecture, specifically targeting the cryptographic authentication mechanisms that protect sensitive operations within the TEE. This weakness arises from the insufficiently protected challenge-response mechanism used to authenticate cryptographic tokens, creating a pathway for attackers to bypass authentication requirements when they possess both root access and physical device control. The vulnerability directly impacts the fundamental security model of Android's secure hardware components, where the TEE is designed to provide a trusted environment for handling sensitive cryptographic operations and key material. The flaw manifests when the system uses a weak challenge that can be easily replayed by malicious actors who have already captured valid responses from previous authentications, effectively allowing unauthorized access to TEE-protected resources.
The technical implementation of this vulnerability stems from the cryptographic protocol design within Android's TEE framework, where the challenge-response authentication mechanism fails to properly randomize or validate the challenge components used in the authentication process. This weakness allows attackers to capture legitimate authentication responses and replay them against the TEE system at a later time, effectively impersonating authorized users without possessing the actual cryptographic keys or credentials required for proper authentication. The vulnerability specifically affects the AuthTokens mechanism that governs access to cryptographic operations within the TEE, where the system relies on a predictable or insufficiently randomized challenge to verify the authenticity of the authentication attempt. According to CWE standards, this represents a weakness in cryptographic implementation classified as CWE-310, specifically related to weak cryptographic randomness or insufficient entropy in challenge generation, which directly enables the authentication bypass scenario.
The operational impact of this vulnerability extends beyond simple unauthorized access to include potential compromise of all cryptographic operations protected by the TEE, including secure key storage, cryptographic signature verification, and protected data encryption. Attackers with root and physical access can leverage this vulnerability to gain unauthorized access to applications and services that depend on TEE-protected cryptographic functions, potentially leading to complete compromise of the device's security posture. The confirmed exploitation on the LG Nexus 5X device demonstrates that this vulnerability affects real-world implementations of Android's security architecture, making it a significant concern for organizations relying on Android devices for security-sensitive operations. This vulnerability particularly impacts enterprise environments where mobile devices handle sensitive corporate data, as it allows attackers to bypass the security controls that should prevent unauthorized access to encrypted data and cryptographic operations.
Mitigation strategies for this vulnerability require immediate system updates and patches from device manufacturers, as the flaw exists at the core Android security architecture level rather than in individual applications. Organizations should implement comprehensive device management policies that ensure timely security updates are deployed across all Android devices, particularly those handling sensitive information. The vulnerability also highlights the importance of physical security controls, as the attack requires root access and physical device control, making it essential for organizations to implement robust physical security measures for mobile devices. Additionally, security teams should conduct thorough assessments of applications that rely on TEE-protected cryptographic functions to identify potential attack vectors and implement additional security controls where necessary. This vulnerability aligns with ATT&CK techniques related to privilege escalation and credential access, specifically targeting the use of legitimate credentials for unauthorized access to protected system resources. Organizations should also consider implementing network-level monitoring to detect anomalous authentication patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper cryptographic protocol design and the need for thorough security testing of core system components before deployment.