CVE-2016-7912 in Android
Summary
by MITRE • 01/25/2023
Use-after-free vulnerability in the ffs_user_copy_worker function in drivers/usb/gadget/function/f_fs.c in the Linux kernel before 4.5.3 allows local users to gain privileges by accessing an I/O data structure after a certain callback call.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability described in CVE-2016-7912 represents a critical use-after-free condition within the Linux kernel's USB gadget function implementation, specifically in the ffs_user_copy_worker function located in drivers/usb/gadget/function/f_fs.c. This flaw exists in kernel versions prior to 4.5.3 and demonstrates a classic memory safety issue that can be exploited by local attackers to escalate privileges. The vulnerability stems from improper handling of memory references where an I/O data structure is accessed after it has been freed, creating a window of opportunity for malicious code execution. The affected component is part of the FunctionFS (Function File System) implementation that provides a filesystem interface for USB gadget functions, making it a core element in USB device emulation capabilities.
The technical exploitation of this vulnerability occurs through a specific sequence where the ffs_user_copy_worker function processes I/O operations and subsequently frees memory resources while other code paths may still reference these structures. This race condition allows an attacker to manipulate the freed memory before it is properly deallocated, potentially leading to arbitrary code execution with kernel privileges. The use-after-free condition (cwe-416) is particularly dangerous because it can be leveraged to achieve privilege escalation, as the attacker can control the memory layout and potentially inject malicious code into kernel space. The vulnerability is classified under the attack pattern of privilege escalation through memory corruption, aligning with ATT&CK technique T1068 which covers exploit for privilege escalation.
The operational impact of this vulnerability extends beyond simple local privilege escalation, as it affects systems running affected kernel versions and can be exploited by any local user with access to the system. The attack vector requires local system access but does not require network connectivity, making it particularly concerning for environments where local access is possible or where users might be tricked into executing malicious code. Systems utilizing USB gadget functionality, particularly those implementing FunctionFS, are at risk, including embedded systems, servers, and devices that support USB device emulation. The exploitation process typically involves careful memory manipulation to ensure that the freed structure can be reused in a controlled manner to achieve code execution. This vulnerability highlights the importance of proper memory management in kernel space and demonstrates how seemingly isolated function calls can create cascading security issues.
Mitigation strategies for CVE-2016-7912 primarily focus on kernel version updates to 4.5.3 or later, which contain the necessary patches to address the use-after-free condition. Organizations should implement comprehensive patch management processes to ensure timely deployment of kernel updates across all systems. Additional defensive measures include monitoring for suspicious local activity and implementing system hardening practices that limit local user privileges where possible. The vulnerability also underscores the need for thorough code review processes focusing on memory management in kernel modules and the importance of static and dynamic analysis tools in identifying similar issues. Security teams should also consider implementing kernel memory protection mechanisms such as stack canaries and address space layout randomization to make exploitation more difficult. Regular security assessments of kernel components and adherence to security best practices for kernel development can help prevent similar vulnerabilities from being introduced in future versions.