CVE-2019-9444 in Android
Summary
by MITRE
In the Android kernel in sync debug fs driver there is a kernel pointer leak due to the usage of printf with %p. This could lead to local information disclosure with system execution privileges needed. User interaction is not needed for exploitation.
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Analysis
by VulDB Data Team • 12/13/2023
The vulnerability identified as CVE-2019-9444 resides within the Android kernel's sync debug filesystem driver, representing a critical information disclosure flaw that exposes kernel memory addresses to unauthorized users. This vulnerability specifically manifests through improper handling of kernel pointers during debugging operations, where the printf function is invoked with the %p format specifier to display memory addresses. The sync debug filesystem driver serves as a mechanism for debugging synchronization primitives within the kernel, but its implementation contains a fundamental flaw that inadvertently leaks kernel virtual addresses to userspace processes. The vulnerability is classified under CWE-209, which describes "Information Exposure Through an Error Message" and specifically relates to improper handling of kernel memory pointers in debug interfaces. This type of information disclosure can provide attackers with crucial insights into kernel memory layout and structure, potentially enabling more sophisticated attacks against the system.
The technical exploitation of this vulnerability requires only local system execution privileges, eliminating the need for complex user interaction or network access. When the sync debug filesystem driver processes certain debug operations, it fails to properly sanitize kernel pointers before outputting them through printf with %p formatting. This allows userspace processes to directly read kernel memory addresses that should remain protected within the kernel's memory space. The leak occurs during normal kernel debugging operations when debugfs entries are accessed, making the vulnerability particularly dangerous as it can be triggered through routine system operations. The %p format specifier in printf is designed to output kernel pointers in a readable format, but in this case, it inadvertently exposes the actual memory addresses where kernel data structures reside. This type of information leak is categorized under the ATT&CK technique T1005, which involves OS credential dumping and information gathering through kernel memory access.
The operational impact of CVE-2019-9444 extends beyond simple information disclosure, as leaked kernel pointers can be leveraged by attackers to bypass kernel address space layout randomization defenses and perform more advanced exploitation techniques. While the vulnerability itself does not directly enable code execution, it significantly reduces the security posture of the affected Android devices by providing attackers with detailed information about kernel memory organization. This information can be used to craft more effective exploits against other vulnerabilities present in the system, particularly those that require precise memory addressing or kernel pointer manipulation. The vulnerability affects Android devices running kernel versions prior to the patch, with the specific affected kernel versions typically including Android 9.0 and earlier releases. Attackers can exploit this vulnerability to gather kernel memory layouts, which can then be used in conjunction with other exploits to achieve privilege escalation or complete system compromise. The lack of user interaction requirements makes this vulnerability particularly concerning for mobile environments where users may not be aware of the underlying kernel operations being performed.
Mitigation strategies for CVE-2019-9444 primarily involve updating to patched kernel versions that properly sanitize kernel pointers before displaying them in debug interfaces. Android security patches released in 2019 addressed this vulnerability by modifying the sync debug filesystem driver to prevent direct pointer exposure through printf operations. System administrators should ensure that all Android devices are updated to the latest security patches, particularly those released in the Q1 2019 timeframe. Additionally, organizations should implement monitoring systems to detect unusual access patterns to debug filesystem entries, as this can serve as an indicator of exploitation attempts. The vulnerability highlights the importance of proper kernel debugging interface design and the need for careful handling of kernel memory addresses in user-facing debug output. Security teams should also consider implementing kernel module integrity checks and memory protection mechanisms to prevent unauthorized access to kernel memory addresses even when such leaks occur. The fix typically involves modifying the debugfs driver to use alternative formatting methods that do not directly expose kernel pointers, thereby preventing the information disclosure while maintaining debugging functionality.