CVE-2021-39773 in Android
Summary
by MITRE • 03/30/2022
In VpnManagerService, there is a possible disclosure of installed VPN packages due to side channel information disclosure. This could lead to local information disclosure with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-12LAndroid ID: A-191276656
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Analysis
by VulDB Data Team • 04/02/2022
The vulnerability identified as CVE-2021-39773 resides within the VpnManagerService component of Android 12L operating systems, representing a significant information disclosure weakness that undermines system security boundaries. This flaw manifests through side channel information disclosure mechanisms within the VPN management service, where installed VPN packages can be inadvertently exposed to unauthorized accessors. The vulnerability specifically affects the Android 12L platform and is catalogued under Android ID A-191276656, indicating its classification within Google's internal vulnerability tracking system. The security implications extend beyond simple data exposure as this vulnerability operates without requiring any additional execution privileges or user interaction, making it particularly dangerous in environments where unauthorized access could occur through legitimate system interfaces.
The technical root cause of this vulnerability stems from improper access controls and information flow management within the VpnManagerService implementation. When the system handles VPN package information, it fails to properly isolate or restrict access to installed VPN applications, creating a side channel that allows unauthorized processes to extract package metadata. This side channel exploitation occurs through legitimate system calls and service interfaces that should normally maintain proper access boundaries between different system components and user applications. The flaw essentially creates an information leakage pathway where the service inadvertently exposes package names, identifiers, or other metadata associated with installed VPN applications without adequate authorization checks. This type of vulnerability aligns with CWE-200 (Information Exposure) and CWE-284 (Improper Access Control) categories, demonstrating how insufficient privilege enforcement can lead to unauthorized information disclosure.
The operational impact of CVE-2021-39773 extends beyond simple information exposure as it provides potential attackers with valuable reconnaissance data that could be leveraged for more sophisticated attacks. The disclosure of installed VPN packages creates a detailed inventory of security tools and applications that users have installed, which could be used to tailor subsequent attacks or identify potential vulnerabilities in specific VPN implementations. This information can be particularly valuable for threat actors seeking to understand a device's security posture or to craft targeted attacks against specific VPN applications. The vulnerability's exploitation requires no additional privileges, meaning that any local process or application with access to the VpnManagerService can potentially extract this information, creating a broad attack surface. From an attacker's perspective, this vulnerability represents a low-effort, high-value information gathering mechanism that could be automated and integrated into broader reconnaissance frameworks.
Mitigation strategies for this vulnerability should focus on implementing proper access controls and information flow restrictions within the VpnManagerService component. System administrators and security teams should ensure that all Android 12L devices are updated with the latest security patches from Google, as this vulnerability has been addressed in subsequent releases. The recommended approach involves strengthening privilege checks and ensuring that package information is only accessible to authorized system components or processes with legitimate need for such information. Additionally, security monitoring should be implemented to detect unauthorized access attempts to VPN management services, and regular security audits should verify that proper access controls are maintained. This vulnerability demonstrates the critical importance of maintaining proper information flow controls in system services and aligns with ATT&CK technique T1083 (File and Directory Discovery) and T1566 (Phishing) where such information disclosure can enable further attacks. Organizations should also consider implementing device enrollment and management policies that enforce security updates and monitor for unauthorized access patterns that could indicate exploitation attempts.