CVE-2016-7908 in QEMU
Summary
by MITRE
The mcf_fec_do_tx function in hw/net/mcf_fec.c in QEMU (aka Quick Emulator) does not properly limit the buffer descriptor count when transmitting packets, which allows local guest OS administrators to cause a denial of service (infinite loop and QEMU process crash) via vectors involving a buffer descriptor with a length of 0 and crafted values in bd.flags.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-7908 resides within the QEMU hypervisor's network interface implementation, specifically in the mcf_fec_do_tx function located in hw/net/mcf_fec.c. This flaw represents a critical security issue that affects virtualized environments where QEMU serves as the underlying emulation platform. The vulnerability stems from inadequate input validation and buffer management within the Fast Ethernet Controller implementation, creating a pathway for malicious actors to exploit the system through crafted packet transmissions.
The technical flaw manifests when the mcf_fec_do_tx function fails to properly validate the buffer descriptor count during packet transmission operations. Under normal circumstances, the function should enforce strict limits on buffer descriptors to prevent memory corruption and system instability. However, the implementation lacks proper bounds checking when processing buffer descriptors with zero length fields and specially crafted bd.flags values. This absence of validation creates a scenario where malicious input can trigger an infinite loop within the transmission processing logic, causing the QEMU process to consume excessive CPU resources and eventually crash.
The operational impact of this vulnerability extends beyond simple denial of service, as it provides local guest OS administrators with the capability to disrupt the entire virtualization environment. When exploited, the vulnerability causes QEMU processes to enter infinite loops that can exhaust system resources and potentially affect other virtual machines running on the same host. The crash behavior represents a significant threat to system availability, particularly in cloud computing environments where multiple VMs share the same physical infrastructure. This vulnerability directly impacts the integrity of virtualized network communications and can be leveraged to create persistent service disruption.
From a cybersecurity perspective, this vulnerability aligns with CWE-129, which addresses improper validation of array index and buffer bounds, and represents a classic example of insufficient input validation in network processing components. The ATT&CK framework categorizes this as a privilege escalation technique through system resource exhaustion, as local guest administrators can leverage this flaw to affect the host system's operational stability. The vulnerability demonstrates the critical importance of input validation in hypervisor components, as network processing functions represent high-value targets for exploitation due to their continuous operation and privileged access patterns.
Mitigation strategies should focus on immediate patch deployment for QEMU versions containing this vulnerability, as well as implementing additional monitoring for anomalous network processing patterns within virtualized environments. System administrators should consider implementing resource limits and process monitoring to detect and prevent the infinite loop conditions that arise from this vulnerability. The fix typically involves adding proper bounds checking for buffer descriptor counts and implementing validation mechanisms for bd.flags values to prevent the exploitation vectors that trigger the infinite loop behavior. Organizations should also conduct comprehensive vulnerability assessments of their virtualization infrastructure to identify similar flaws in other network controller implementations and ensure proper input validation across all hypervisor components.