CVE-2021-39648 in Android
Summary
by MITRE • 12/15/2021
In gadget_dev_desc_UDC_show of configfs.c, there is a possible disclosure of kernel heap memory due to a race condition. This could lead to local information disclosure with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-160822094References: Upstream kernel
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Analysis
by VulDB Data Team • 12/18/2021
The vulnerability identified as CVE-2021-39648 resides within the Android kernel's configfs.c implementation, specifically in the gadget_dev_desc_UDC_show function. This flaw represents a critical information disclosure vulnerability that stems from an improper handling of kernel heap memory access during concurrent operations. The issue manifests as a race condition that allows unauthorized access to sensitive kernel memory contents, potentially exposing confidential data stored within the kernel heap. The vulnerability affects Android kernel versions and has been documented with the Android ID A-160822094, with upstream kernel references indicating this is a well-known issue in kernel configuration file systems.
The technical root cause of this vulnerability lies in the improper synchronization mechanisms within the gadget_dev_desc_UDC_show function, which handles device descriptor information in the USB gadget configuration. When multiple threads or processes attempt to access the same kernel memory region simultaneously, the race condition allows for memory corruption or unintended data exposure. This type of vulnerability falls under CWE-362, which specifically addresses race conditions in software systems where concurrent access to shared resources leads to unpredictable behavior. The flaw occurs during the configuration file system operations where USB gadget device descriptions are displayed, creating an opportunity for attackers to extract kernel heap contents that should remain protected from user-space access.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with potential access to sensitive kernel memory that could contain cryptographic keys, session tokens, or other confidential data. An attacker with system execution privileges can exploit this vulnerability to gain unauthorized access to kernel heap memory contents, potentially leading to privilege escalation or further exploitation of the system. The local nature of this vulnerability means that an attacker must already possess system execution privileges, but once exploited, the information disclosure could enable more sophisticated attacks. This vulnerability aligns with ATT&CK technique T1003.002, which involves OS credential dumping, as the exposed kernel memory may contain authentication-related data or system secrets.
Mitigation strategies for CVE-2021-39648 should focus on implementing proper synchronization mechanisms within the affected kernel functions to prevent concurrent access to shared memory regions. System administrators should ensure that all Android kernel updates are applied promptly, particularly those addressing upstream kernel configuration file system vulnerabilities. The fix typically involves adding proper locking mechanisms or atomic operations to prevent race conditions during memory access operations. Additionally, kernel hardening measures such as stack canaries, kernel address space layout randomization, and memory protection mechanisms should be enabled to reduce the overall attack surface. Regular security audits of kernel configuration files and USB gadget implementations should be conducted to identify similar race condition vulnerabilities that could potentially lead to information disclosure or privilege escalation attacks.