CVE-2020-36313 in Linux
Summary
by MITRE • 04/07/2021
An issue was discovered in the Linux kernel before 5.7. The KVM subsystem allows out-of-range access to memslots after a deletion, aka CID-0774a964ef56. This affects arch/s390/kvm/kvm-s390.c, include/linux/kvm_host.h, and virt/kvm/kvm_main.c.
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Analysis
by VulDB Data Team • 04/11/2021
The vulnerability identified as CVE-2020-36313 represents a critical memory management flaw within the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem, specifically affecting versions prior to 5.7. This issue manifests as an out-of-range memory access condition that occurs during the deletion of memory slots, creating a potential vector for privilege escalation and system instability. The vulnerability impacts the s390 architecture implementation of KVM, making it particularly concerning for mainframe and enterprise environments that rely on this virtualization technology. The affected code paths span across multiple kernel components including the s390-specific KVM implementation, the kernel virtual machine host headers, and the core KVM main implementation files, indicating a fundamental flaw in how memory slot management is handled during deletion operations.
The technical root cause of this vulnerability stems from improper handling of memory slot references within the KVM subsystem's memory management framework. When a memory slot is deleted from the virtual machine's memory configuration, the system fails to properly invalidate or clear references to that memory region before the deletion process completes. This creates a window where subsequent memory access operations can reference memory locations that have already been freed or reallocated, leading to potential memory corruption, data leakage, or arbitrary code execution. The flaw is categorized as a memory safety issue that directly relates to CWE-125, which describes out-of-bounds read conditions, and CWE-787, which covers out-of-bounds write vulnerabilities. The vulnerability's impact is amplified by the fact that it occurs within the kernel's virtualization layer, meaning that an attacker with access to a guest virtual machine could potentially exploit this condition to escape the virtualization boundary and gain elevated privileges on the host system.
The operational impact of CVE-2020-36313 extends beyond simple system crashes or memory corruption, as it creates opportunities for persistent exploitation within virtualized environments. Attackers can leverage this vulnerability to perform privilege escalation attacks, potentially moving from guest VM execution context to host kernel privileges, which would compromise the entire virtualization infrastructure. This vulnerability particularly affects systems running KVM on s390 architecture platforms, including IBM z/VM and related mainframe virtualization environments where the KVM subsystem is heavily utilized. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the T1068 - Exploitation for Privilege Escalation tactic. Organizations with extensive virtualization deployments, particularly those using KVM for containerization or cloud infrastructure, face significant risk exposure from this vulnerability, as it could enable attackers to gain unauthorized access to sensitive data or disrupt critical services.
Mitigation strategies for CVE-2020-36313 primarily focus on immediate kernel version upgrades to 5.7 or later, which contain the necessary patches to address the memory slot deletion handling issue. System administrators should prioritize patching affected systems, particularly those running KVM virtualization on s390 architecture platforms, as the vulnerability can be exploited remotely by authenticated attackers within guest VMs. Additional mitigations include implementing strict virtual machine access controls, monitoring for unusual memory access patterns, and maintaining updated security configurations. Organizations should also consider isolating critical virtualized workloads and implementing network segmentation to limit potential attack surfaces. The vulnerability's classification as a kernel-level memory management flaw means that traditional network security measures may be insufficient, requiring deeper system-level monitoring and hardening approaches. Regular vulnerability assessments and security audits should be conducted to ensure complete remediation of this and similar memory safety issues within the virtualization stack.