CVE-2018-9840 in Open Whisper Signal App
Summary
by MITRE
The Open Whisper Signal app before 2.23.2 for iOS allows physically proximate attackers to bypass the screen locker feature via certain rapid sequences of actions that include app opening, clicking on cancel, and using the home button.
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Analysis
by VulDB Data Team • 02/27/2023
The Open Whisper Signal application version 2.23.1 and earlier for iOS contained a critical security flaw that compromised the application's screen lock mechanism through a specifically crafted sequence of user interactions. This vulnerability exploited a fundamental weakness in the application's session management and lock screen implementation, allowing attackers with physical access to the device to bypass the intended security controls. The flaw was particularly concerning as it targeted the core security feature designed to protect sensitive communication data when the application was not actively in use.
The technical implementation of this vulnerability stemmed from improper handling of application lifecycle events and state transitions within the iOS environment. Attackers could execute a rapid sequence involving opening the Signal application, immediately clicking the cancel button, and then pressing the home button to return to the device's main screen. This specific combination of actions exploited a race condition or state management flaw where the application failed to properly re-engage its screen lock protection mechanism. The vulnerability was classified under the Common Weakness Enumeration as a weakness related to improper handling of application state transitions and session management, specifically falling under CWE-665 improper initialization of a resource.
The operational impact of this vulnerability was significant as it effectively neutralized the screen lock protection that Signal intended to provide to its users. This weakness allowed unauthorized individuals with physical access to a device to potentially access encrypted messages and communications without proper authentication. The attack vector was particularly dangerous because it required minimal technical knowledge and could be executed rapidly, making it suitable for casual exploitation in environments where physical proximity to the target device was achievable. This vulnerability directly impacted the confidentiality and integrity of communications that Signal users expected to be protected by the application's security model, potentially exposing sensitive information to unauthorized parties.
The mitigation strategy for this vulnerability required updating to Signal application version 2.23.2 or later, which implemented proper state management and session handling to prevent the exploitation sequence. Security researchers recommended that users immediately update their Signal applications to the patched version to ensure continued protection of their communications. Additionally, users should maintain awareness of the security implications of physical device access and consider implementing additional security measures such as strong device-level authentication and encryption. This vulnerability highlighted the importance of proper application lifecycle management and the need for comprehensive testing of state transitions in mobile applications. The issue also demonstrated how seemingly minor implementation flaws in security-critical applications could lead to significant compromises in user privacy and data protection, aligning with attack patterns documented in the MITRE ATT&CK framework under application security and mobile security domains. Organizations and individuals relying on Signal for secure communications should ensure all devices are updated to versions that address this vulnerability to maintain the intended security posture of the application.