CVE-2018-9567 in Android
Summary
by MITRE
On Pixel devices there is a bug causing verified boot to show the same certificate fingerprint despite using different signing keys. This may lead to local escalation of privilege if people are relying on those fingerprints to determine what version of the OS the device is running, with System execution privileges needed. User interaction is not needed for exploitation. Product: Android. Versions: Android kernel. Android ID: A-65543936.
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Analysis
by VulDB Data Team • 04/18/2020
The vulnerability described in CVE-2018-9567 represents a critical flaw in the Android Verified Boot implementation specifically affecting Pixel devices. This security weakness stems from a fundamental issue in how the system handles certificate fingerprint verification during the boot process, creating a scenario where different signing keys can produce identical fingerprint outputs. The flaw exists within the Android kernel and affects the core security mechanism responsible for ensuring device integrity and authenticating system components during startup. The vulnerability demonstrates a clear failure in cryptographic verification processes that should distinguish between legitimate and malicious system updates.
The technical nature of this vulnerability lies in the broken certificate fingerprint generation mechanism within the verified boot process. When multiple signing keys are used to sign system images, the system should produce distinct fingerprint values that can be used to verify the authenticity and version of the running operating system. However, this vulnerability causes the system to generate identical fingerprints regardless of which signing key was actually used, effectively undermining the entire verification mechanism. This issue falls under CWE-327, which addresses broken cryptographic algorithms, and specifically relates to weak cryptographic hashing or certificate generation flaws. The vulnerability operates at the kernel level, requiring system execution privileges for exploitation, which means an attacker with local access could potentially leverage this weakness to gain elevated privileges.
The operational impact of this vulnerability is severe as it creates a false sense of security for users and systems that rely on certificate fingerprint verification to determine OS authenticity. Attackers could exploit this weakness to install malicious system components that appear to be legitimate updates, as the fingerprint verification would pass despite the compromised software. The vulnerability is particularly dangerous because it does not require user interaction for exploitation, making it a passive threat that can be leveraged by attackers without any direct user engagement. This characteristic aligns with ATT&CK technique T1068, which involves local privilege escalation through kernel exploits, and represents a significant risk to device security and integrity. The flaw essentially allows attackers to bypass critical security checks that should prevent unauthorized system modifications.
Mitigation strategies for CVE-2018-9567 should focus on both immediate patching and enhanced monitoring of system verification processes. Device manufacturers should implement immediate firmware updates that correct the certificate fingerprint generation algorithm to ensure distinct outputs for different signing keys. System administrators should implement additional verification layers beyond simple fingerprint checks, including hash verification of system components and enhanced logging of boot process activities. Organizations should also consider implementing behavioral monitoring to detect anomalous boot patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper cryptographic implementation and the need for robust testing of security mechanisms before deployment. Given its classification as a kernel-level vulnerability, users should ensure their devices receive timely security updates and should avoid installing unofficial system modifications that might interfere with the verified boot process.