CVE-2018-20125 in QEMU
Summary
by MITRE
hw/rdma/vmw/pvrdma_cmd.c in QEMU allows attackers to cause a denial of service (NULL pointer dereference or excessive memory allocation) in create_cq_ring or create_qp_rings.
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Analysis
by VulDB Data Team • 10/26/2024
The vulnerability identified as CVE-2018-20125 resides within the QEMU virtualization platform's implementation of the VMware paravirtualized RDMA (pvrdma) device driver. This flaw manifests in the hw/rdma/vmw/pvrdma_cmd.c source file where improper input validation and memory management handling creates exploitable conditions that can lead to system instability. The vulnerability specifically affects the create_cq_ring and create_qp_rings functions which are responsible for allocating and configuring completion queues and queue pairs within the virtual RDMA device implementation. These functions process commands from guest operating systems that attempt to establish RDMA communication channels, making them critical components in the virtualized network stack.
The technical exploitation of this vulnerability occurs through malformed or crafted commands sent to the pvrdma device driver during the initialization phase of RDMA operations. When an attacker submits specially constructed parameters to the create_cq_ring or create_qp_rings functions, the code fails to properly validate input parameters before proceeding with memory allocation operations. This validation gap can result in either a NULL pointer dereference when the code attempts to access uninitialized or improperly allocated memory structures, or alternatively triggers excessive memory allocation patterns that can exhaust system resources. The flaw stems from inadequate bounds checking and parameter validation within the command processing pipeline, allowing malicious inputs to bypass normal input sanitization mechanisms that should prevent invalid memory operations.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise the stability and availability of virtualized environments. When a NULL pointer dereference occurs, it typically results in a kernel panic or process termination that can crash the entire virtual machine or even the host system if the vulnerability is exploited in a privileged context. The excessive memory allocation scenario can lead to memory exhaustion conditions that prevent legitimate operations from completing successfully, effectively creating a resource exhaustion attack that degrades system performance or renders the virtualized environment unusable. This vulnerability is particularly concerning in cloud computing and virtualization environments where multiple tenants share the same physical infrastructure, as a single compromised guest could potentially impact other virtual machines running on the same host.
Mitigation strategies for CVE-2018-20125 should focus on both immediate patching and operational hardening measures. The primary solution involves applying the official QEMU patch that implements proper input validation and parameter checking in the affected functions, ensuring that all memory allocation operations are preceded by comprehensive bounds checking and null pointer validation. Organizations should also implement monitoring solutions that can detect anomalous command sequences or memory allocation patterns that may indicate exploitation attempts. From a defensive perspective, implementing network segmentation and access controls around virtualization infrastructure can limit the attack surface, while regular security assessments of virtualized environments should include verification of QEMU component versions and patch status. This vulnerability aligns with CWE-476 which addresses NULL pointer dereference conditions, and represents a typical example of how improper input validation in device drivers can create critical system stability issues that affect virtualized computing environments. The ATT&CK framework categorizes this as a privilege escalation and denial of service technique that can be leveraged in virtual machine escape scenarios, making it particularly relevant for organizations operating cloud-based or containerized environments where virtualization security is paramount.