CVE-2021-39640 in Android
Summary
by MITRE • 12/15/2021
In __dwc3_gadget_ep0_queue of ep0.c, there is a possible out of bounds write due to improper locking. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-157294279References: N/A
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 12/18/2021
The vulnerability identified as CVE-2021-39640 resides within the Android kernel's USB gadget driver implementation, specifically in the dwc3_gadget_ep0_queue function located in the ep0.c file. This flaw represents a critical security weakness that could potentially enable local privilege escalation without requiring any additional execution privileges or user interaction for exploitation. The vulnerability stems from improper locking mechanisms within the USB gadget endpoint zero queueing function, which is responsible for managing the control endpoint operations in the USB device controller.
The technical flaw manifests as an out-of-bounds write condition that occurs when multiple threads or processes attempt to access the USB gadget endpoint zero queue simultaneously without proper synchronization. This improper locking allows for race conditions where concurrent operations can overwrite memory locations beyond the intended buffer boundaries. The underlying issue is classified as a CWE-119 vulnerability, which encompasses memory access issues including out-of-bounds writes, and falls under the broader category of improper locking mechanisms that can lead to memory corruption. The absence of adequate mutex or spinlock protection during critical sections of code execution creates a window where malicious or legitimate concurrent access can result in memory corruption that compromises system integrity.
The operational impact of this vulnerability extends beyond simple memory corruption as it provides a pathway for local privilege escalation. An attacker with local access to an affected Android device could potentially leverage this flaw to elevate their privileges from a regular user context to a root or system-level context. This represents a significant security risk as it eliminates the need for additional attack vectors or user interaction, making exploitation straightforward and potentially automated. The vulnerability affects the Android kernel directly, meaning any device running an affected kernel version could be compromised, including smartphones, tablets, and other Android-based devices that utilize the dwc3 USB controller hardware.
Mitigation strategies for CVE-2021-39640 should focus on implementing proper locking mechanisms within the dwc3 gadget driver code to prevent concurrent access to the endpoint zero queue operations. Security patches should introduce adequate synchronization primitives such as mutex locks or spinlocks around the critical sections of the dwc3_gadget_ep0_queue function. The fix should ensure that all access to the endpoint queue structures is properly serialized to prevent race conditions that lead to out-of-bounds memory writes. Organizations should prioritize applying vendor-provided security updates and kernel patches that address this specific locking implementation issue. Additionally, system administrators should monitor for any unauthorized local access to affected devices and consider implementing additional security controls such as device integrity verification and runtime monitoring to detect potential exploitation attempts. The vulnerability aligns with ATT&CK technique T1068, which involves exploiting local privileges, and represents a clear pathway for attackers to escalate their privileges within the Android operating system environment.