CVE-2018-9452 in Android
Summary
by MITRE
In getOffsetForHorizontal of Layout.java, there is a possible application hang due to a slow width calculation. This could lead to remote denial of service if a contact with many hidden unicode characters were sent to the device and used by a local app, with no additional execution privileges needed. User interaction is needed for exploitation. Product: Android Versions: Android-7.0 Android-7.1.1 Android-7.1.2 Android-8.0 Android-8.1 Android-9.0 Android ID: A-78464361
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 03/29/2020
The vulnerability identified as CVE-2018-9452 represents a critical denial of service weakness in Android's layout rendering system that specifically affects the getOffsetForHorizontal method within the Layout.java file. This flaw manifests as an application hang condition that occurs during the calculation of text width for horizontal layout operations, creating a scenario where maliciously crafted input can cause significant performance degradation and system instability. The vulnerability is classified under CWE-400 as an Uncontrolled Resource Consumption issue, where the computational complexity of width calculation increases exponentially with certain input patterns, particularly those containing numerous hidden unicode characters that are not immediately visible to users.
The technical implementation of this vulnerability stems from the way Android's text rendering engine processes unicode character sequences during layout calculations. When the getOffsetForHorizontal method encounters contact data or text containing many hidden or non-printable unicode characters, the width calculation algorithm becomes computationally expensive, potentially leading to indefinite blocking of the rendering thread. This occurs because the system must process each character individually through the layout engine, and certain unicode sequences trigger inefficient processing paths that can take considerable time to complete. The vulnerability operates at the application level within the Android framework's text rendering capabilities, specifically affecting the Android 7.0 through 9.0 versions, making it particularly concerning given the widespread adoption of these Android versions across various devices.
The operational impact of this vulnerability extends beyond simple application hanging, as it creates a potential remote denial of service vector that can be exploited without requiring elevated privileges or additional execution rights. An attacker can craft malicious contact data containing numerous hidden unicode characters and transmit it to a target device, where a local application that processes this data will trigger the vulnerable code path. The exploitation requires user interaction, typically through the acceptance of the malicious contact data, but once triggered, the vulnerability can cause complete system responsiveness issues. This aligns with ATT&CK technique T1499.001 for Network Denial of Service and represents a significant risk to user experience and device stability. The vulnerability affects any application that utilizes the Android layout system for text rendering, particularly those handling user contact data, SMS messages, or other text-based inputs.
Mitigation strategies for CVE-2018-9452 focus on both immediate defensive measures and long-term architectural improvements to prevent similar issues in the future. Android security patches implemented by Google addressed this vulnerability by optimizing the width calculation algorithms and adding input sanitization to prevent excessive unicode character processing during layout operations. Organizations should ensure their Android devices are updated to the latest security patches, which include modifications to the Layout.java file that prevent the exponential time complexity during width calculations. Additionally, developers should implement proper input validation in their applications, particularly when processing user-generated content that may contain unicode characters, by limiting the number of hidden characters processed in layout calculations. The vulnerability demonstrates the importance of robust input validation and resource consumption limits in text rendering systems, as outlined in security best practices for mobile application development. Security teams should monitor for similar patterns in other text processing components and consider implementing automated testing for unicode character sequences that may trigger performance degradation in layout systems.