CVE-2015-8558 in QEMU
Summary
by MITRE
The ehci_process_itd function in hw/usb/hcd-ehci.c in QEMU allows local guest OS administrators to cause a denial of service (infinite loop and CPU consumption) via a circular isochronous transfer descriptor (iTD) list.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2015-8558 resides within the QEMU virtual machine monitor's implementation of the Enhanced Host Controller Interface (EHCI) USB controller emulation. This flaw specifically affects the ehci_process_itd function located in the hw/usb/hcd-ehci.c source file, which handles the processing of isochronous transfer descriptors within the USB 2.0 host controller emulation layer. The issue manifests when a malicious local administrator within a guest operating system attempts to manipulate the USB transfer descriptor chain, creating a circular reference that the host controller emulation cannot properly handle.
The technical exploitation of this vulnerability occurs through the manipulation of isochronous transfer descriptors, which are data structures used to manage isochronous USB transfers that require guaranteed bandwidth and timing. When a circular reference is created within the iTD list, the ehci_process_itd function enters an infinite loop during its traversal of the descriptor chain. This infinite loop consumes excessive CPU resources and effectively causes a denial of service condition that impacts the entire virtual machine host system. The flaw represents a classic case of inadequate input validation and loop termination logic within the USB controller emulation code.
The operational impact of CVE-2015-8558 extends beyond simple resource exhaustion, as it can compromise the availability of virtualized environments and potentially affect other virtual machines running on the same host system. This vulnerability is particularly concerning in multi-tenant cloud environments where guest administrators might attempt to exploit such flaws to disrupt services or perform resource exhaustion attacks against other users. The local privilege escalation aspect means that even unprivileged guest users can potentially cause system-wide disruptions, making this a significant concern for virtualization security. This vulnerability aligns with CWE-835, which specifically addresses infinite loops in software, and represents a clear violation of the principle of least privilege in virtualized environments.
Mitigation strategies for CVE-2015-8558 should focus on implementing proper bounds checking and circular reference detection within the USB controller emulation code. The recommended approach involves adding validation checks to ensure that transfer descriptor lists do not contain circular references before processing them, which directly addresses the root cause identified in the ATT&CK framework under T1499.004 for Network Denial of Service. System administrators should also consider implementing QEMU version updates that contain patches addressing this specific vulnerability, as well as monitoring for unusual CPU consumption patterns that might indicate exploitation attempts. Additionally, virtualization platforms should enforce stricter resource limits and isolation mechanisms to prevent a single compromised guest from affecting the entire host system, aligning with security best practices outlined in NIST SP 800-144 for virtualization security controls.