CVE-2016-8910 in QEMU
Summary
by MITRE
The rtl8139_cplus_transmit function in hw/net/rtl8139.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (infinite loop and CPU consumption) by leveraging failure to limit the ring descriptor count.
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Analysis
by VulDB Data Team • 09/29/2022
The vulnerability identified as CVE-2016-8910 resides within the QEMU virtualization platform's network driver implementation, specifically in the rtl8139_cplus_transmit function located in hw/net/rtl8139.c. This issue affects the virtualized network interface controller that emulates the Realtek RTL8139 chipset, which is commonly used in virtual machine environments. The flaw represents a critical security concern that demonstrates how virtualization software can be exploited to create resource exhaustion conditions that impact the overall system stability and performance.
The technical root cause of this vulnerability stems from inadequate input validation and boundary checking within the transmit function of the emulated network adapter. When a guest operating system administrator manipulates the ring descriptor count beyond acceptable limits, the function fails to properly validate these parameters, leading to an infinite loop condition in the transmit processing code. This condition causes the virtual machine's CPU resources to be consumed continuously, effectively creating a denial of service scenario that can impact not only the affected virtual machine but potentially the entire host system. The vulnerability operates at the hypervisor level, making it particularly dangerous as it can be exploited by users with administrative privileges within the guest operating system.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader system stability concerns. An attacker with local administrative access within a guest OS can trigger this condition to consume excessive CPU cycles, potentially leading to resource starvation for other virtual machines running on the same host. This scenario creates a vector for resource exhaustion attacks that can degrade overall performance or cause complete system unresponsiveness, particularly in multi-tenant environments where multiple virtual machines share the same physical hardware resources. The infinite loop condition specifically targets the transmit processing path, which is frequently used in network communication scenarios, making the exploitation particularly effective.
Mitigation strategies for CVE-2016-8910 should focus on both immediate patching and defensive configuration measures. The primary solution involves applying the official QEMU patch that implements proper bounds checking on ring descriptor counts within the rtl8139_cplus_transmit function, which directly addresses the underlying validation flaw. Organizations should also implement monitoring systems to detect unusual CPU consumption patterns that might indicate exploitation attempts. Additionally, network segmentation and access controls should be enforced to limit the privileges available to guest OS administrators, reducing the attack surface. From a defensive perspective, this vulnerability aligns with CWE-129, which covers improper validation of array indices, and can be mapped to ATT&CK technique T1499.001 for resource exhaustion attacks. The vulnerability demonstrates the importance of proper input validation in virtualization software components and highlights the need for comprehensive security testing of hypervisor-level code to prevent similar issues in other network driver implementations.