CVE-2016-9776 in QEMU
Summary
by MITRE
QEMU (aka Quick Emulator) built with the ColdFire Fast Ethernet Controller emulator support is vulnerable to an infinite loop issue. It could occur while receiving packets in 'mcf_fec_receive'. A privileged user/process inside guest could use this issue to crash the QEMU process on the host leading to DoS.
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Analysis
by VulDB Data Team • 10/13/2022
The vulnerability CVE-2016-9776 represents a critical denial of service flaw in QEMU's ColdFire Fast Ethernet Controller emulator implementation. This issue manifests within the mcf_fec_receive function where an infinite loop condition can be triggered by malicious packet processing. The vulnerability specifically affects QEMU installations that have been compiled with ColdFire Fast Ethernet Controller support, making it a targeted issue for systems utilizing this particular emulation feature. The flaw exists at the intersection of virtualization security and network protocol handling, where guest operating systems can exploit improper packet validation mechanisms to cause host-level disruptions.
The technical root cause of this vulnerability lies in the insufficient input validation within the mcf_fec_receive function of QEMU's network emulation layer. When processing incoming network packets, the function fails to properly handle malformed or specially crafted packet structures that can cause the execution flow to enter an infinite loop. This occurs because the packet processing logic does not adequately check packet boundaries, length fields, or other critical packet attributes that could lead to recursive or repeated processing conditions. The vulnerability is particularly dangerous because it requires only a privileged user or process within the guest operating system to exploit, making it accessible through normal guest execution paths rather than requiring elevated privileges at the host level.
From an operational impact perspective, this vulnerability creates a significant risk for virtualized environments where QEMU is used for system emulation or virtual machine hosting. A malicious user within a guest operating system can deliberately craft network packets that trigger the infinite loop condition, causing the QEMU process to consume excessive CPU resources and eventually crash. This leads to complete denial of service for the affected virtual machine and potentially impacts the entire host system if multiple VMs are running concurrently. The vulnerability essentially allows for a guest-to-host privilege escalation in terms of system availability, where a low-privilege guest user can cause high-privilege host-level disruptions.
The vulnerability aligns with CWE-835, which covers infinite loops in software implementations, and demonstrates how network protocol handling can create execution flow issues that lead to denial of service conditions. From an ATT&CK framework perspective, this represents a privilege escalation technique through resource exhaustion and a denial of service attack vector that leverages guest-level access to compromise host system availability. The attack surface is particularly concerning in cloud computing environments and virtualization platforms where multiple tenants share the same host infrastructure, as this vulnerability could be used to disrupt other virtual machines running on the same physical host. Mitigation strategies include updating QEMU to versions that address the infinite loop condition, implementing network traffic filtering at the guest level, and applying runtime protections that monitor for abnormal CPU usage patterns that might indicate the exploit execution.
This vulnerability highlights the importance of thorough input validation in virtualization software, particularly in network emulation components that handle untrusted data from guest operating systems. The flaw demonstrates how seemingly minor implementation issues in protocol handling can create significant security risks in virtualized environments where guest and host systems share resources and execution contexts. Organizations using QEMU for virtualization should prioritize patching this vulnerability and implementing monitoring systems that can detect and alert on abnormal resource consumption patterns that might indicate exploitation attempts.