CVE-2018-20126 in QEMU
Summary
by MITRE
hw/rdma/vmw/pvrdma_cmd.c in QEMU allows create_cq and create_qp memory leaks because errors are mishandled.
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Analysis
by VulDB Data Team • 10/26/2024
The vulnerability identified as CVE-2018-20126 resides within the QEMU hypervisor's implementation of RDMA (Remote Direct Memory Access) virtualization components, specifically in the pvrdma_cmd.c file that handles VMware's pvrdma device emulation. This issue manifests as memory leak conditions that occur during the creation of completion queues and queue pairs, fundamental data structures used in RDMA operations for managing asynchronous events and communication channels between virtual machines and hardware. The flaw represents a classic resource management error where the hypervisor fails to properly release allocated memory when error conditions occur during the creation process, leading to progressive memory consumption over time.
The technical root cause stems from improper error handling mechanisms within the QEMU RDMA subsystem, where the create_cq and create_qp functions do not adequately clean up previously allocated memory resources when subsequent operations fail. This memory leak pattern follows CWE-401: Improper Release of Memory and aligns with ATT&CK technique T1484 which involves resource exhaustion through memory manipulation. When virtual machines attempt to create RDMA completion queues or queue pairs, the system allocates memory for these structures but fails to deallocate them properly upon error conditions, creating a persistent memory leak that can accumulate over multiple operations.
The operational impact of this vulnerability extends beyond simple memory consumption, as it can lead to significant performance degradation and potential system instability in virtualized environments. An attacker or malicious actor could exploit this vulnerability by repeatedly triggering the creation of RDMA resources, causing progressive memory exhaustion on the host system and potentially leading to denial of service conditions. This vulnerability particularly affects environments running QEMU with RDMA virtualization enabled, where multiple virtual machines might be actively utilizing RDMA capabilities for high-performance networking operations. The memory leaks accumulate over time, potentially causing the host system to become unresponsive or crash when memory resources are depleted.
Mitigation strategies for CVE-2018-20126 involve applying the official QEMU security patches that correct the error handling logic in the pvrdma_cmd.c file, ensuring that all allocated memory is properly freed regardless of error conditions during resource creation. System administrators should also implement monitoring solutions to track memory usage patterns in virtualized environments and establish alerting mechanisms for unusual memory consumption trends. Additionally, organizations should consider disabling RDMA virtualization features in QEMU when they are not actively required, reducing the attack surface and potential impact of such memory leak vulnerabilities. The fix should be validated through comprehensive testing to ensure that legitimate RDMA operations continue to function correctly while eliminating the memory leak conditions that allow for progressive resource exhaustion.