CVE-2017-7493 in QEMU
Summary
by MITRE
Quick Emulator (Qemu) built with the VirtFS, host directory sharing via Plan 9 File System(9pfs) support, is vulnerable to an improper access control issue. It could occur while accessing virtfs metadata files in mapped-file security mode. A guest user could use this flaw to escalate their privileges inside guest.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-7493 affects Quick Emulator (QEMU) when configured with VirtFS and 9pfs support, representing a critical access control flaw that undermines the security boundaries between guest and host systems. This issue specifically manifests in the mapped-file security mode of VirtFS implementation, where improper access controls allow malicious guest users to exploit metadata file access patterns. The vulnerability stems from insufficient validation of file access permissions within the Plan 9 File System implementation, creating a pathway for privilege escalation attacks that can compromise the entire virtualized environment.
The technical flaw resides in how QEMU handles file metadata operations within the VirtFS subsystem when operating under mapped-file security mode. When guest users attempt to access files through the 9pfs interface, the system fails to properly enforce access controls on metadata files that contain critical information about file ownership, permissions, and access patterns. This improper access control mechanism allows authenticated guest users to manipulate or read metadata files that should remain restricted to the host system, effectively bypassing the isolation that virtualization environments are designed to provide. The vulnerability is classified under CWE-284, which specifically addresses improper access control issues in software systems.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally compromises the security model of virtualized environments. Guest users who exploit this flaw can gain elevated privileges within the guest operating system, potentially leading to complete system compromise. The attack vector becomes particularly dangerous when considering that many virtualized environments rely on the assumption that guest users cannot access host resources or escalate privileges beyond their intended scope. This vulnerability enables attackers to move laterally within the virtualized infrastructure, potentially accessing sensitive data or using the compromised guest as a foothold for attacking other systems in the network.
Security practitioners should implement multiple layers of mitigation strategies to address this vulnerability effectively. The immediate solution involves updating QEMU to versions that contain patches addressing the improper access control issue, as recommended by the vendor and security advisories. Organizations should also consider disabling VirtFS functionality when not required, or implementing additional access controls at the host level to limit guest access to critical system resources. Network segmentation and monitoring of virtualized environments can help detect anomalous access patterns that might indicate exploitation attempts. This vulnerability aligns with ATT&CK technique T1055, which covers privilege escalation through exploitation of software vulnerabilities, and demonstrates the critical importance of maintaining up-to-date virtualization software to prevent attackers from leveraging known flaws in hypervisor implementations.