CVE-2016-9576 in Linux
Summary
by MITRE • 01/25/2023
The blk_rq_map_user_iov function in block/blk-map.c in the Linux kernel before 4.8.14 does not properly restrict the type of iterator, which allows local users to read or write to arbitrary kernel memory locations or cause a denial of service (use-after-free) by leveraging access to a /dev/sg device.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2016-9576 resides within the Linux kernel's block layer implementation, specifically in the blk_rq_map_user_iov function located in block/blk-map.c. This flaw represents a critical security issue that affects Linux kernel versions prior to 4.8.14, creating a pathway for local attackers to exploit kernel memory access controls. The vulnerability stems from insufficient validation of iterator types during the mapping of user-space I/O operations to kernel memory structures, fundamentally undermining the kernel's memory safety mechanisms.
The technical root cause of this vulnerability lies in the improper handling of iterator validation within the block request mapping process. When a user process accesses a /dev/sg device, which provides access to SCSI generic devices, the kernel's blk_rq_map_user_iov function fails to adequately restrict the type of iterator being used. This oversight allows malicious code to manipulate the iterator parameters in such a way that they can bypass kernel memory protection boundaries. The vulnerability specifically enables attackers to perform arbitrary read and write operations against kernel memory addresses, effectively breaking the kernel's memory isolation guarantees.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it creates multiple attack vectors for local adversaries. An attacker with access to a /dev/sg device can leverage this flaw to either read sensitive kernel memory contents, potentially extracting cryptographic keys, credentials, or other confidential information, or to write to arbitrary kernel memory locations, which could result in system crashes or even complete system compromise. The use-after-free condition that can occur represents a particularly dangerous aspect, as it allows for memory corruption that may enable privilege escalation attacks or denial of service scenarios that could persist until system reboot.
This vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and CWE-787, which covers out-of-bounds write conditions, both of which are directly enabled by the improper iterator type validation. From an ATT&CK framework perspective, this vulnerability maps to T1068, which involves the exploitation of local privilege escalation opportunities, and T1499, which covers network denial of service attacks through system resource exhaustion. The attack surface is primarily limited to local users with access to SCSI generic devices, but the implications are severe due to the potential for kernel memory corruption and privilege escalation.
The recommended mitigation strategy involves upgrading to Linux kernel version 4.8.14 or later, where the vulnerability has been addressed through proper iterator type validation and enhanced memory access controls. Additionally, system administrators should consider restricting access to /dev/sg devices to minimize potential attack vectors, though this represents a partial mitigation rather than a complete solution. Organizations should also implement monitoring for unusual I/O patterns or memory access attempts that could indicate exploitation attempts. The fix implemented in the patched kernel version ensures proper validation of iterator parameters and prevents the bypass of kernel memory protection mechanisms that was previously possible through the flawed blk_rq_map_user_iov function.