CVE-2015-6855 in QEMU
Summary
by MITRE
hw/ide/core.c in QEMU does not properly restrict the commands accepted by an ATAPI device, which allows guest users to cause a denial of service or possibly have unspecified other impact via certain IDE commands, as demonstrated by a WIN_READ_NATIVE_MAX command to an empty drive, which triggers a divide-by-zero error and instance crash.
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Analysis
by VulDB Data Team • 06/15/2022
The vulnerability identified as CVE-2015-6855 resides within the QEMU virtualization platform's IDE controller implementation, specifically in the hw/ide/core.c file. This flaw represents a critical security issue that affects virtualized environments where ATAPI (ATA Packet Interface) devices are utilized. The vulnerability stems from insufficient command validation within the IDE subsystem, creating a pathway for malicious guest operating systems to exploit the hypervisor through crafted IDE commands.
The technical implementation of this vulnerability involves the improper restriction of commands accepted by ATAPI devices within the QEMU virtual machine monitor. When a guest operating system sends a WIN_READ_NATIVE_MAX command to an empty IDE drive, the hypervisor fails to properly validate this command against the device state. This validation failure results in a divide-by-zero error condition that crashes the QEMU instance, effectively causing a denial of service attack against the virtual machine. The flaw specifically impacts the handling of ATAPI commands where the system does not properly check whether the command is appropriate for the current device state or configuration.
From an operational perspective, this vulnerability enables guest users to execute remote code execution attacks that can compromise the entire virtualization host. The impact extends beyond simple denial of service as the divide-by-zero error can potentially be leveraged for more sophisticated attacks, including privilege escalation or information disclosure. The vulnerability affects all QEMU versions prior to the patched release, making it a widespread concern for virtualized environments that rely on IDE controller emulation. Attackers can exploit this through standard guest-to-host communication channels, making it particularly dangerous in multi-tenant cloud environments where isolation is paramount.
The vulnerability aligns with CWE-248, which addresses "Uncaught Exception" in software systems, and can be mapped to ATT&CK technique T1059.001 for command and scripting interpreter. The lack of proper input validation in the ATAPI command processing creates an attack surface that can be exploited through standard virtual machine escape techniques. Organizations using QEMU-based virtualization platforms must consider this vulnerability as part of their broader security posture, particularly in environments where guest isolation is critical for maintaining security boundaries between virtual machines.
Mitigation strategies should include immediate patching of QEMU installations to versions that address the command validation issue. System administrators should also implement network segmentation and access controls to limit guest user privileges within virtual environments. Additional defensive measures include monitoring for unusual IDE command patterns and implementing virtual machine resource limits to prevent single compromised guests from affecting the entire host system. Organizations should also consider implementing hypervisor-level security controls and regularly auditing virtual machine configurations to ensure proper isolation boundaries are maintained.