CVE-2020-13754 in QEMU
Summary
by MITRE
hw/pci/msix.c in QEMU 4.2.0 allows guest OS users to trigger an out-of-bounds access via a crafted address in an msi-x mmio operation.
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Analysis
by VulDB Data Team • 10/26/2024
The vulnerability identified as CVE-2020-13754 resides within the QEMU virtual machine monitor's handling of MSI-X (Message Signaled Interrupts Extended) functionality, specifically in the hw/pci/msix.c file version 4.2.0. This represents a critical security flaw that enables malicious guest operating systems to exploit memory access patterns beyond the intended boundaries. The issue manifests when a guest OS performs crafted memory-mapped I/O operations targeting MSI-X configuration registers, allowing for unauthorized memory access that could potentially lead to information disclosure or system compromise.
The technical root cause of this vulnerability stems from insufficient input validation and boundary checking within the MSI-X handling code. When processing MSI-X memory operations, the QEMU implementation fails to properly validate address ranges and offsets, creating a scenario where a crafted address within the MSI-X MMIO space can reference memory locations outside the allocated buffer boundaries. This out-of-bounds memory access occurs during the processing of MSI-X table entries and vector control registers, where the guest OS can manipulate address fields to traverse memory regions that should remain protected from direct guest access. The flaw operates at the virtualization layer, specifically affecting how QEMU manages PCI MSI-X interrupts for virtualized environments.
The operational impact of CVE-2020-13754 extends beyond simple memory corruption, as it creates potential pathways for privilege escalation and information disclosure within virtualized environments. An attacker controlling a guest OS can leverage this vulnerability to read or write to arbitrary memory locations within the QEMU process address space, potentially accessing sensitive data from other virtual machines or the host system. This vulnerability particularly affects systems running QEMU version 4.2.0 and earlier, where the MSI-X implementation lacks proper bounds checking mechanisms. The attack vector requires a malicious guest OS to be running on the same hypervisor, making it a significant concern for multi-tenant cloud environments where guest isolation is paramount.
Mitigation strategies for CVE-2020-13754 should prioritize immediate patching of QEMU installations to version 4.2.1 or later, which contains the necessary fixes for the MSI-X boundary checking implementation. Organizations should also implement network segmentation and access controls to limit guest OS privileges, particularly in multi-tenant environments where guest isolation is critical. The vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and represents a specific instance of improper access control in virtualized environments. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and credential access through exploitation of hypervisor vulnerabilities, specifically targeting the virtualization layer to gain unauthorized system access.
The remediation process requires careful consideration of virtual machine configurations and patch management protocols to ensure all QEMU instances are updated consistently across the infrastructure. Security teams should monitor for potential exploitation attempts and implement additional logging mechanisms to detect suspicious MSI-X memory operations. Organizations utilizing QEMU-based virtualization platforms must conduct thorough vulnerability assessments to identify systems running affected versions and prioritize patch deployment to prevent exploitation. The fix implemented in subsequent QEMU releases addresses the core validation issue by adding proper boundary checks to MSI-X MMIO operations, ensuring that guest OS memory accesses remain within valid address ranges and preventing out-of-bounds memory access patterns that could be exploited by malicious actors.