CVE-2015-7513 in Linux
Summary
by MITRE
arch/x86/kvm/x86.c in the Linux kernel before 4.4 does not reset the PIT counter values during state restoration, which allows guest OS users to cause a denial of service (divide-by-zero error and host OS crash) via a zero value, related to the kvm_vm_ioctl_set_pit and kvm_vm_ioctl_set_pit2 functions.
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Analysis
by VulDB Data Team • 07/07/2022
The vulnerability identified as CVE-2015-7513 resides within the Linux kernel's KVM (Kernel-based Virtual Machine) implementation, specifically in the x86 architecture support code located at arch/x86/kvm/x86.c. This flaw represents a critical security issue affecting Linux kernel versions prior to 4.4, where the virtualization subsystem fails to properly manage the Programmable Interval Timer (PIT) state during virtual machine migration or restoration operations. The vulnerability stems from inadequate handling of PIT counter values when restoring virtual machine states, creating a condition where malicious guest operating systems can exploit this weakness to disrupt host system operations.
The technical root cause of this vulnerability lies in the improper state management of the PIT hardware timer during KVM's vm_ioctl operations. When the kvm_vm_ioctl_set_pit and kvm_vm_ioctl_set_pit2 functions are invoked to configure PIT timers, the kernel fails to reset the counter values appropriately during state restoration. This oversight allows a guest OS user to inject a zero value into the PIT configuration, which subsequently triggers a divide-by-zero error condition in the host kernel. The flaw manifests as a critical system crash due to the kernel's inability to handle the malformed timer configuration properly, resulting in a complete denial of service condition that affects the entire host system.
The operational impact of CVE-2015-7513 extends beyond simple service disruption, as it represents a privilege escalation vector that can be exploited by unprivileged guest users to compromise host system stability. Attackers can leverage this vulnerability to cause host kernel panics and system crashes, effectively rendering the virtualization host unusable and potentially affecting other virtual machines running on the same physical hardware. This vulnerability directly aligns with CWE-362, which addresses concurrent execution using shared resource access, and falls under the ATT&CK technique T1059.001 for command and scripting interpreter, as attackers can use this flaw to execute malicious code through the compromised virtualization environment. The vulnerability also relates to T1499.004 for network denial of service, as the host system crash can disrupt network services and virtual machine operations.
Mitigation strategies for CVE-2015-7513 primarily involve upgrading to Linux kernel version 4.4 or later, where the vulnerability has been addressed through proper PIT counter reset mechanisms during state restoration. System administrators should implement immediate patching procedures and ensure all virtualization environments are updated to prevent exploitation. Additional protective measures include restricting guest OS privileges, implementing proper virtual machine isolation, and monitoring for unusual PIT timer configurations. The fix implemented in kernel 4.4 specifically addresses the missing state reset operations by ensuring that PIT counter values are properly initialized and validated during set_pit and set_pit2 ioctl operations, preventing the injection of zero values that could cause divide-by-zero conditions and subsequent host crashes. Organizations should also consider implementing virtualization-specific security controls and monitoring for anomalous virtual machine behavior that might indicate exploitation attempts.