CVE-2016-6836 in QEMU
Summary
by MITRE
The vmxnet3_complete_packet function in hw/net/vmxnet3.c in QEMU (aka Quick Emulator) allows local guest OS administrators to obtain sensitive host memory information by leveraging failure to initialize the txcq_descr object.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-6836 resides within the vmxnet3 network driver implementation in QEMU virtualization software, specifically in the hw/net/vmxnet3.c file. This flaw represents a critical information disclosure vulnerability that affects virtualized environments where guest operating systems have administrative privileges. The issue manifests through the vmxnet3_complete_packet function which fails to properly initialize the txcq_descr object during packet processing operations, creating a potential pathway for unauthorized memory access.
The technical root cause of this vulnerability stems from inadequate memory initialization within the virtual network adapter's transmit completion queue descriptor structure. When guest operating systems execute administrative commands or network operations, the vmxnet3 driver fails to properly clear or initialize memory regions within the txcq_descr object. This incomplete initialization leaves residual data from previous operations in memory locations that should be cleared, potentially exposing sensitive host memory contents to the guest environment. The vulnerability is particularly concerning because it operates at the hypervisor level where guest administrators could exploit this weakness to gain insights into host memory structures, potentially leading to more sophisticated attacks.
From an operational impact perspective, this vulnerability creates a significant security risk for virtualized environments where guest operating systems might be compromised or where malicious administrators have elevated privileges. The disclosure of host memory information could enable attackers to understand memory layout patterns, identify security mechanisms, or even extract sensitive data from the host system. This information leakage could facilitate privilege escalation attacks, memory corruption exploitation, or other advanced persistent threats that leverage knowledge of host memory structures. The vulnerability affects QEMU versions prior to 2.7.0, making it a widespread concern for organizations running older virtualization infrastructure.
The vulnerability aligns with CWE-119, which addresses "Improper Access to Memory Location" and relates to improper initialization of memory structures. It also connects to ATT&CK technique T1059, specifically "Command and Scripting Interpreter" where attackers might use information disclosure to gain deeper system knowledge. Additionally, this flaw demonstrates characteristics of T1082, "System Information Discovery," where attackers seek to understand system memory layout and configuration. The vulnerability represents a classic case of insufficient input validation and memory management in virtualization components, where the failure to properly initialize data structures creates exploitable conditions for information leakage.
Organizations should implement immediate mitigations by upgrading to QEMU version 2.7.0 or later where this vulnerability has been addressed through proper memory initialization practices. System administrators should also consider implementing additional monitoring for unusual memory access patterns or network behavior that might indicate exploitation attempts. Network segmentation and access control measures should be reinforced to limit guest administrative privileges where possible. Regular security assessments of virtualization environments should include checks for similar memory initialization vulnerabilities in other hypervisor components and network drivers. The fix implemented in QEMU 2.7.0 specifically addresses the uninitialized memory issue by ensuring proper initialization of the txcq_descr object before it is used in packet completion operations, thereby preventing the leakage of sensitive host memory information to guest operating systems.