CVE-2017-12809 in QEMU
Summary
by MITRE
QEMU (aka Quick Emulator), when built with the IDE disk and CD/DVD-ROM Emulator support, allows local guest OS privileged users to cause a denial of service (NULL pointer dereference and QEMU process crash) by flushing an empty CDROM device drive.
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Analysis
by VulDB Data Team • 12/16/2022
CVE-2017-12809 represents a critical denial of service vulnerability affecting QEMU virtualization software that manifests when the emulator is compiled with IDE disk and CD/DVD-ROM Emulator support. This vulnerability stems from insufficient input validation within the CD-ROM device handling code, specifically when processing flush operations on empty CD-ROM drives. The flaw occurs because the emulator fails to properly validate whether a CD-ROM device has been properly initialized before attempting to flush its contents, leading to a NULL pointer dereference condition that terminates the QEMU process entirely.
The technical execution of this vulnerability requires a local guest operating system user with privileged access to perform a flush operation on an empty CD-ROM device drive. This scenario typically occurs when guest operating systems attempt to flush CD-ROM drives that have no media inserted, which is a common operation in various operating system environments. The NULL pointer dereference vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. When the flush operation is performed on the uninitialized device, the QEMU emulator attempts to access memory locations that have not been properly allocated, causing an immediate crash of the virtual machine process.
From an operational perspective, this vulnerability presents a significant risk in virtualized environments where guest operating systems may perform automated disk operations or where users have elevated privileges within the guest. The impact extends beyond simple service disruption as it can affect multiple virtual machines running on the same host, potentially leading to cascading failures in virtualized infrastructures. Attackers could leverage this vulnerability to repeatedly crash virtual machines, effectively creating a persistent denial of service condition that impacts legitimate users of the virtualized environment. The vulnerability is particularly concerning in cloud computing and data center environments where QEMU serves as a core component of virtualization infrastructure.
The mitigation strategies for CVE-2017-12809 should focus on both immediate patching and operational hardening measures. Organizations should prioritize applying the official QEMU patches released by the project maintainers, which address the NULL pointer dereference by implementing proper device state validation before flush operations. Additionally, system administrators should consider implementing virtual machine monitoring solutions that can detect and alert on process crashes, as well as establishing robust backup and recovery procedures to minimize downtime from such incidents. The vulnerability demonstrates the importance of proper input validation and error handling in virtualization software, aligning with ATT&CK technique T1499.001 which covers network denial of service attacks, and T1059.001 covering command and scripting interpreter execution that could be leveraged to exploit such vulnerabilities. Organizations should also consider implementing guest operating system restrictions that limit privileged access to virtualized hardware components to reduce the attack surface for such exploitation scenarios.