CVE-2016-8909 in QEMU
Summary
by MITRE
The intel_hda_xfer function in hw/audio/intel-hda.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (infinite loop and CPU consumption) via an entry with the same value for buffer length and pointer position.
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Analysis
by VulDB Data Team • 09/29/2022
The vulnerability identified as CVE-2016-8909 resides within the QEMU virtualization platform's audio subsystem, specifically in the intel_hda_xfer function located in hw/audio/intel-hda.c. This issue affects the Intel High Definition Audio controller implementation used by QEMU to emulate audio hardware for virtual machines. The flaw represents a classic buffer management error that can be exploited by local administrators within the guest operating system to disrupt normal system operations. The vulnerability stems from inadequate validation of audio buffer parameters during data transfer operations, creating a condition where malicious input can trigger unexpected behavior in the emulation layer.
The technical implementation of this vulnerability involves a specific condition where an audio buffer entry contains identical values for both buffer length and pointer position fields. When this occurs, the intel_hda_xfer function fails to properly handle the edge case, leading to an infinite loop in the audio data transfer mechanism. The function enters a state where it continuously processes the same buffer position without advancing the pointer, causing sustained CPU utilization that can effectively deny service to other system processes. This type of vulnerability falls under the CWE-835 category of infinite loops or infinite recursion, where a loop condition fails to properly terminate, consuming system resources indefinitely.
The operational impact of CVE-2016-8909 extends beyond simple resource exhaustion, as it can severely degrade the performance of virtualized environments where QEMU is deployed. Local guest administrators can leverage this vulnerability to perform denial of service attacks against their own virtual machines or potentially impact other VMs running on the same host system. The attack vector requires local access within the guest OS, making it less severe than remote exploits but still dangerous in multi-tenant virtualization environments where guest isolation is critical. The vulnerability can be particularly problematic in cloud computing environments where multiple customers share the same hypervisor infrastructure, as a malicious user could potentially disrupt service for other tenants.
Mitigation strategies for this vulnerability should focus on both immediate patching and operational hardening measures. The primary solution involves applying the official QEMU patch that corrects the buffer length and pointer position validation logic within the intel_hda_xfer function. Organizations should also implement monitoring systems to detect unusual CPU consumption patterns that might indicate exploitation attempts. From a defense-in-depth perspective, virtualization administrators should consider implementing guest OS hardening measures and limiting administrative privileges within virtual machines. The ATT&CK framework categorizes this type of vulnerability exploitation under T1499.004 - Endpoint Denial of Service, where adversaries leverage system vulnerabilities to consume resources. Additionally, implementing proper input validation and boundary checking in audio subsystems aligns with security best practices outlined in NIST SP 800-160 and ISO/IEC 27001 standards for secure system development and operation.