CVE-2018-20191 in QEMU
Summary
by MITRE
hw/rdma/vmw/pvrdma_main.c in QEMU does not implement a read operation (such as uar_read by analogy to uar_write), which allows attackers to cause a denial of service (NULL pointer dereference).
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 10/26/2024
The vulnerability identified as CVE-2018-20191 resides within the QEMU virtualization platform's implementation of VMware Paravirtualized RDMA (pvrdma) hardware emulation component. This flaw specifically affects the hw/rdma/vmw/pvrdma_main.c file where the developers failed to implement a proper read operation counterpart to the existing write functionality. The pvrdma device emulation is designed to provide high-performance RDMA (Remote Direct Memory Access) capabilities within virtualized environments, enabling efficient network communication between virtual machines and host systems. The absence of a complete read operation implementation creates a critical gap in the device's functionality that can be exploited by malicious actors.
The technical nature of this vulnerability manifests as a NULL pointer dereference condition that occurs when the system attempts to execute a read operation on the pvrdma device without proper initialization or validation. When an attacker crafts a malicious read request to the device's memory-mapped registers or communication interfaces, the system attempts to access memory locations that have not been properly allocated or initialized. This results in a kernel-level NULL pointer dereference which inevitably leads to a system crash or denial of service condition. The vulnerability stems from an incomplete implementation where only the write functionality was properly coded while the corresponding read operations were omitted or inadequately handled.
The operational impact of this vulnerability extends beyond simple service disruption as it represents a serious security concern within virtualized environments. In cloud computing and enterprise virtualization deployments, where QEMU serves as a foundational hypervisor component, this flaw could enable attackers to perform denial of service attacks against virtual machines or entire host systems. The vulnerability affects systems running QEMU versions prior to the patch release that addressed this specific implementation gap. Attackers could potentially exploit this weakness to crash virtual machines, disrupt service availability, or in more sophisticated scenarios, potentially escalate privileges if the system lacks proper memory protection mechanisms. The flaw particularly impacts environments where RDMA acceleration is enabled, making it a significant concern for high-performance computing and data center virtualization infrastructures.
Mitigation strategies for CVE-2018-20191 primarily focus on updating QEMU to versions that contain the proper read operation implementation and memory management handling for the pvrdma device. System administrators should immediately apply security patches from their respective distribution vendors or directly from the QEMU project maintainers. Additionally, implementing proper access controls and network segmentation can help limit the attack surface by restricting unauthorized access to virtualized environments. The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and may map to ATT&CK technique T1499.004 related to network denial of service attacks. Organizations should also consider implementing monitoring solutions to detect anomalous behavior patterns that might indicate exploitation attempts, particularly around RDMA device access and memory operations. Regular security assessments of virtualization environments are recommended to identify similar incomplete implementation flaws that could lead to system instability or security breaches.