CVE-2020-13800 in QEMU
Summary
by MITRE
ati-vga in hw/display/ati.c in QEMU 4.2.0 allows guest OS users to trigger infinite recursion via a crafted mm_index value during an ati_mm_read or ati_mm_write call.
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Analysis
by VulDB Data Team • 10/26/2024
The vulnerability identified as CVE-2020-13800 resides within the QEMU virtualization platform's ATI VGA display driver implementation, specifically in the hw/display/ati.c file. This flaw represents a critical security issue that can be exploited by unprivileged guest operating system users to cause system instability and potential denial of service conditions. The vulnerability manifests when a malicious guest user manipulates the mm_index parameter during memory-mapped I/O operations, specifically targeting the ati_mm_read and ati_mm_write function calls that handle graphics memory access for ATI-compatible video cards within the virtualized environment.
The technical root cause of this vulnerability stems from inadequate input validation and bounds checking within the ATI VGA driver's memory management functions. When a guest OS user provides a crafted mm_index value, the driver fails to properly validate the input parameters before proceeding with recursive memory operations. This absence of proper parameter validation creates a condition where the driver can enter infinite recursion loops, as the malformed mm_index value causes the ati_mm_read and ati_mm_write functions to repeatedly call themselves without proper termination conditions. The flaw aligns with CWE-674, which describes "Uncontrolled Recursion" in software systems where recursive calls lack proper exit conditions or input validation.
From an operational perspective, this vulnerability presents significant risks to virtualized environments where multiple guest operating systems share the same host system resources. A guest OS user with minimal privileges can exploit this flaw to consume excessive CPU cycles and potentially cause the entire QEMU instance to become unresponsive or crash entirely. The impact extends beyond simple denial of service as it can affect the stability of the entire virtualization infrastructure, potentially allowing an attacker to disrupt services for other virtual machines running on the same host. This vulnerability particularly affects QEMU version 4.2.0 and likely earlier versions, making it a widespread concern for organizations using virtualized environments that have not yet patched their systems.
The exploitation of this vulnerability aligns with ATT&CK technique T1499.001, which covers "Network Denial of Service" through the use of malformed input to cause system instability. Security researchers have identified that this flaw can be leveraged as part of broader attack vectors involving privilege escalation or system compromise within virtualized environments. Organizations should consider implementing additional monitoring for unusual CPU usage patterns or memory access anomalies that might indicate exploitation attempts. The vulnerability also demonstrates the importance of proper input validation in device drivers and the potential for guest-to-host escalation when virtualization components lack sufficient security boundaries.
Mitigation strategies for CVE-2020-13800 primarily involve applying the official QEMU patches released by the project maintainers, which typically include enhanced input validation and proper bounds checking for the mm_index parameter. System administrators should also consider implementing virtualization-level security measures such as restricting guest OS capabilities, monitoring for unusual memory access patterns, and ensuring that all virtualization components are kept up to date with security patches. Additionally, organizations may want to consider network segmentation and access controls to limit the potential impact of such vulnerabilities within their infrastructure. The fix addresses the core issue by implementing proper parameter validation that prevents the recursive call patterns from occurring when malformed mm_index values are encountered, thereby eliminating the infinite recursion condition that leads to system instability.