CVE-2018-7858 in QEMU
Summary
by MITRE
Quick Emulator (aka QEMU), when built with the Cirrus CLGD 54xx VGA Emulator support, allows local guest OS privileged users to cause a denial of service (out-of-bounds access and QEMU process crash) by leveraging incorrect region calculation when updating VGA display.
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Analysis
by VulDB Data Team • 02/21/2023
The vulnerability identified as CVE-2018-7858 affects Quick Emulator QEMU when configured with Cirrus CLGD 54xx VGA Emulator support, representing a critical security flaw that enables local privilege escalation within virtualized environments. This issue manifests when guest operating systems with elevated privileges attempt to manipulate VGA display regions through improper memory access patterns, leading to unpredictable system behavior and potential service disruption. The vulnerability resides in the graphics emulation subsystem where incorrect calculations during VGA region updates create conditions for out-of-bounds memory access that ultimately crashes the QEMU process.
The technical root cause of this vulnerability stems from inadequate boundary checking within the Cirrus CLGD 54xx VGA emulator implementation, specifically in how the emulator calculates and validates memory regions during display updates. When a guest OS attempts to modify VGA display parameters, the emulator fails to properly validate the calculated memory addresses against actual allocated regions, allowing access to memory locations outside the intended boundaries. This flaw falls under CWE-129 Input Validation and CWE-787 Out-of-bounds Write, both of which are fundamental security weaknesses that can lead to system instability and potential exploitation. The improper region calculation occurs during the processing of VGA update commands where memory addresses are computed without sufficient validation of their legitimacy within the allocated display memory space.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be leveraged by malicious actors within compromised guest environments to disrupt virtualized computing infrastructures. Local privileged users in guest operating systems can exploit this weakness to crash the QEMU process, effectively causing a denial of service that affects the entire virtual machine. This vulnerability is particularly concerning in cloud computing environments where multiple virtual machines share underlying physical resources, as a successful exploit could potentially impact other VMs running on the same host. The attack vector requires local access within the guest OS with privileged permissions, making it more difficult to exploit remotely but still dangerous in compromised environments where attackers have already gained elevated privileges.
Mitigation strategies for CVE-2018-7858 should prioritize immediate patch application from QEMU maintainers, as the vulnerability affects core virtualization functionality and cannot be effectively addressed through configuration changes alone. Organizations should implement comprehensive monitoring of QEMU processes and virtual machine stability to detect potential exploitation attempts. The use of hypervisor-level security controls and proper access controls within guest operating systems can help limit the potential impact by reducing the likelihood of privilege escalation within virtualized environments. Additionally, regular security assessments of virtualization infrastructure should include evaluation of graphics emulation components, as this vulnerability demonstrates the importance of validating all memory operations in virtualized graphics subsystems. Security teams should also consider implementing network segmentation and access controls to limit the potential impact of successful exploitation, while maintaining detailed logging of virtual machine activities to detect anomalous behavior indicative of attempted exploitation.