CVE-2016-9922 in QEMU
Summary
by MITRE
The cirrus_do_copy function in hw/display/cirrus_vga.c in QEMU (aka Quick Emulator), when cirrus graphics mode is VGA, allows local guest OS privileged users to cause a denial of service (divide-by-zero error and QEMU process crash) via vectors involving blit pitch values.
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Analysis
by VulDB Data Team • 11/22/2022
The vulnerability identified as CVE-2016-9922 resides within the QEMU virtual machine emulator's cirrus graphics driver implementation, specifically in the cirrus_do_copy function located in hw/display/cirrus_vga.c. This flaw manifests when QEMU operates in cirrus graphics mode with VGA compatibility, presenting a significant security concern for virtualized environments where guest operating systems may have elevated privileges. The vulnerability represents a classic divide-by-zero error condition that can be exploited by local privileged users within the guest OS to crash the QEMU process, effectively causing a denial of service that impacts the entire virtual machine infrastructure.
The technical exploitation of this vulnerability occurs through manipulation of blit pitch values during graphics operations. When a guest OS with sufficient privileges executes specific graphics operations that involve the cirrus_do_copy function, the function fails to properly validate input parameters related to blit pitch values. This validation failure allows an attacker to provide malicious pitch values that result in a division operation with zero as the divisor, triggering an immediate system crash. The flaw demonstrates characteristics consistent with CWE-369: Divide by Zero, which specifically addresses the condition where a division operation uses a zero divisor, leading to program termination. The vulnerability is particularly dangerous in virtualized environments where guest operating systems might be compromised or where users have elevated privileges within the guest.
The operational impact of CVE-2016-9922 extends beyond simple service disruption to encompass broader system stability concerns within virtualized infrastructures. When exploited, the divide-by-zero error causes the QEMU process to terminate abruptly, leading to complete virtual machine crash and potential data loss. This vulnerability affects any system running QEMU with cirrus graphics mode enabled, making it particularly concerning for cloud service providers and organizations relying on virtualization technologies. The attack vector requires local access with guest OS privileges, meaning that the vulnerability is most dangerous in environments where guest isolation is compromised or where users have elevated access rights within the virtual machine. Organizations using QEMU for virtualization, particularly those running multiple virtual machines, face significant risk as a single compromised guest could potentially affect the entire virtualization host.
Mitigation strategies for CVE-2016-9922 primarily involve applying the vendor-provided patches that address the validation issues in the cirrus_do_copy function. System administrators should ensure that all QEMU installations are updated to versions that contain the necessary fixes, typically released as part of the QEMU 2.7.0 release cycle. Additionally, implementing proper input validation and boundary checking within the graphics driver code can prevent similar issues from occurring in the future. Security monitoring should include detection of abnormal graphics operations that might indicate exploitation attempts, while network segmentation and proper access controls can limit the potential impact of privilege escalation within guest environments. Organizations should also consider implementing virtual machine isolation measures and regularly auditing their virtualization infrastructure to ensure that all components are running patched versions. The vulnerability highlights the importance of validating all input parameters in graphics processing functions and demonstrates how seemingly minor flaws in device drivers can result in critical system instability, aligning with ATT&CK technique T1068: Exploitation for Privilege Escalation and T1499: Endpoint Denial of Service in virtualized environments.