CVE-2015-8962 in Android
Summary
by MITRE • 01/25/2023
Double free vulnerability in the sg_common_write function in drivers/scsi/sg.c in the Linux kernel before 4.4 allows local users to gain privileges or cause a denial of service (memory corruption and system crash) by detaching a device during an SG_IO ioctl call.
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Analysis
by VulDB Data Team • 01/25/2023
The CVE-2015-8962 vulnerability represents a critical double free error in the Linux kernel's SCSI generic (sg) subsystem that affects versions prior to 4.4. This flaw exists within the sg_common_write function located in drivers/scsi/sg.c, making it a significant security concern for systems utilizing SCSI devices and the SG_IO ioctl interface. The vulnerability stems from improper memory management during device detachment operations, creating a scenario where the same memory block can be freed twice, leading to unpredictable behavior and potential privilege escalation.
The technical implementation of this vulnerability involves a race condition and memory management flaw that occurs specifically when a device is detached while an SG_IO ioctl call is in progress. During such operations, the kernel's SCSI generic driver fails to properly validate the device state before attempting memory deallocation, resulting in a double free condition. This memory corruption manifests when the sg_common_write function handles write operations to a SCSI generic device, particularly during device removal operations. The flaw is classified under CWE-415 as a double free vulnerability, where the same memory location is deallocated twice, potentially allowing attackers to manipulate heap metadata or execute arbitrary code.
The operational impact of this vulnerability extends beyond simple denial of service to include potential privilege escalation, making it particularly dangerous for local attackers who can leverage this condition to gain elevated system privileges. When exploited, the double free condition can cause memory corruption that may lead to system crashes, kernel panics, or in some cases, allow malicious code execution with kernel-level privileges. The vulnerability is especially concerning in environments where local users have access to SCSI devices or the ability to invoke SG_IO operations, as it provides a direct pathway for privilege escalation. According to ATT&CK framework, this vulnerability maps to T1059.007 (Command and Scripting Interpreter: Python) and T1068 (Exploitation for Privilege Escalation) when attackers leverage local access to exploit the memory corruption for elevated privileges.
Mitigation strategies for CVE-2015-8962 primarily involve updating to Linux kernel version 4.4 or later, where the double free vulnerability has been patched through improved memory management and device state validation. System administrators should also implement proper access controls to limit local user privileges and restrict access to SCSI devices and SG_IO operations where possible. Additionally, monitoring for unusual device detachment patterns and implementing kernel hardening measures such as stack canaries and memory protection mechanisms can help detect and prevent exploitation attempts. Organizations should conduct vulnerability assessments to identify systems running affected kernel versions and prioritize patch deployment to prevent potential exploitation by malicious actors. The fix implemented in kernel 4.4 addresses the root cause by ensuring proper reference counting and device state validation during the SG_IO ioctl processing, preventing the double free condition from occurring during device detachment operations.