CVE-2017-15306 in Linux
Summary
by MITRE
The kvm_vm_ioctl_check_extension function in arch/powerpc/kvm/powerpc.c in the Linux kernel before 4.13.11 allows local users to cause a denial of service (NULL pointer dereference and system crash) via a KVM_CHECK_EXTENSION KVM_CAP_PPC_HTM ioctl call to /dev/kvm.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/06/2023
The vulnerability identified as CVE-2017-15306 represents a critical NULL pointer dereference flaw within the Linux kernel's KVM (Kernel-based Virtual Machine) implementation specifically targeting PowerPC architectures. This issue exists in the kvm_vm_ioctl_check_extension function located in arch/powerpc/kvm/powerpc.c, affecting Linux kernel versions prior to 4.13.11. The flaw manifests when a local user executes a KVM_CHECK_EXTENSION ioctl call with the KVM_CAP_PPC_HTM capability, triggering a system crash through improper validation of input parameters. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with access to the /dev/kvm device, which typically requires minimal privileges on systems with KVM support enabled.
The technical exploitation of this vulnerability follows a well-defined pattern that aligns with CWE-476, which describes NULL pointer dereference conditions. When the KVM_CHECK_EXTENSION ioctl is called with KVM_CAP_PPC_HTM, the function fails to properly validate whether the extension capability is supported before attempting to access memory locations that may be NULL. This particular flaw leverages the PowerPC-specific hardware transactional memory (HTM) capabilities, where the kernel's handling of the KVM_CAP_PPC_HTM extension does not adequately check for proper initialization or support status. The vulnerability demonstrates poor input validation practices and lacks proper null checks in the kernel's virtualization subsystem, creating an exploitable path that leads to immediate system instability and potential denial of service conditions.
The operational impact of CVE-2017-15306 extends beyond simple system crashes, as it represents a significant threat to system availability and stability in virtualized environments. Local attackers can leverage this vulnerability to cause complete system crashes without requiring elevated privileges, effectively creating a denial of service condition that can be exploited repeatedly. The vulnerability is particularly concerning in production environments where multiple users may have access to the /dev/kvm device, as it allows for unprivileged code execution that results in system-wide crashes. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 (Network Denial of Service) and T1068 (Exploitation for Privilege Escalation), though the latter is less applicable given that the attack requires only local access. The flaw essentially allows for a form of privilege escalation through system instability rather than direct privilege elevation, though it can be leveraged by attackers to disrupt services and create persistent availability issues.
Mitigation strategies for CVE-2017-15306 center around immediate kernel version upgrades to 4.13.11 or later, which contain the necessary patches to address the NULL pointer dereference issue. System administrators should prioritize patching affected systems, particularly those running PowerPC-based virtualization environments where KVM is utilized. Additional mitigations include restricting access to /dev/kvm device through proper file system permissions, ensuring that only trusted users or processes can interact with the KVM subsystem. Organizations should also implement monitoring solutions to detect unusual patterns of KVM ioctl calls that might indicate exploitation attempts. The fix implemented in the patched kernel versions addresses the root cause by adding proper null checks and validation before attempting to access memory locations associated with the KVM_CAP_PPC_HTM capability, aligning with security best practices for kernel-level input validation and defensive programming principles.