CVE-2017-5669 in Linux
Summary
by MITRE
The do_shmat function in ipc/shm.c in the Linux kernel through 4.9.12 does not restrict the address calculated by a certain rounding operation, which allows local users to map page zero, and consequently bypass a protection mechanism that exists for the mmap system call, by making crafted shmget and shmat system calls in a privileged context.
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Analysis
by VulDB Data Team • 02/24/2017
The vulnerability identified as CVE-2017-5669 represents a critical flaw in the Linux kernel's shared memory implementation that undermines fundamental security protections designed to prevent unauthorized memory access. This issue resides within the do_shmat function located in ipc/shm.c of the Linux kernel version 4.9.12 and earlier, where the kernel fails to properly constrain address calculations during shared memory mapping operations. The flaw specifically manifests when the kernel performs a rounding operation during shared memory address determination, creating an opportunity for local attackers to manipulate memory mappings in ways that were not intended by the system's security architecture.
The technical mechanism behind this vulnerability involves the improper handling of address calculations within the shared memory subsystem. When a privileged process executes shmget and shmat system calls in sequence, the kernel's rounding operation can result in an address that maps to page zero of the virtual address space. This particular memory page is typically protected by the kernel's mmap system call protection mechanisms, which are designed to prevent mapping of the zero page to maintain system integrity and security boundaries. However, due to the flaw in address calculation, attackers can bypass these protections by carefully crafting their shared memory allocation and attachment operations to force the kernel into mapping page zero, thereby circumventing the intended security controls.
The operational impact of CVE-2017-5669 is significant as it provides local attackers with a means to bypass critical kernel-level protections that are fundamental to maintaining system security. This vulnerability enables privilege escalation scenarios where an unprivileged user could potentially gain elevated privileges by exploiting the ability to map page zero and manipulate memory mappings in ways that should be restricted. The attack requires local access to a system with a vulnerable kernel version, but once successful, it can allow attackers to circumvent security controls that are essential for maintaining the integrity of the kernel's memory management subsystem. The vulnerability particularly affects systems where privileged processes execute shared memory operations, making it relevant to various system services and applications that rely on shared memory mechanisms for inter-process communication.
This vulnerability aligns with CWE-125, which describes "Out-of-bounds Read" conditions, and more specifically relates to improper address validation within kernel memory management. From an attack perspective, the flaw corresponds to techniques described in the ATT&CK framework under T1068, which covers "Local Privilege Escalation" through kernel exploits, and T1059, which encompasses "Command and Scripting Interpreter" techniques used in exploitation. The vulnerability demonstrates how seemingly minor flaws in kernel memory management can have profound implications for system security, as the improper rounding operation creates a pathway for bypassing memory protection mechanisms that are fundamental to preventing unauthorized access to system resources. Organizations should prioritize patching systems running vulnerable kernel versions, as this flaw represents a significant risk to system integrity and could potentially be leveraged in more sophisticated attack scenarios involving privilege escalation and memory manipulation. The fix for this vulnerability involved implementing proper address range validation and ensuring that the rounding operation in the shared memory subsystem properly constrains the resulting memory mappings to prevent access to protected memory regions.