CVE-2016-9602 in QEMU
Summary
by MITRE
Qemu before version 2.9 is vulnerable to an improper link following when built with the VirtFS. A privileged user inside guest could use this flaw to access host file system beyond the shared folder and potentially escalating their privileges on a host.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 11/01/2022
The vulnerability identified as CVE-2016-9602 represents a critical security flaw in QEMU virtualization software that affects versions prior to 2.9. This issue specifically manifests when QEMU is compiled with VirtFS (Virtual File System) support, creating a pathway for privilege escalation and unauthorized host system access. The vulnerability stems from inadequate path resolution mechanisms within the VirtFS implementation, which fails to properly validate or sanitize file paths when processing guest requests. This improper link following behavior allows malicious actors to exploit symbolic link traversal techniques that bypass intended access controls.
The technical exploitation of this vulnerability occurs through the manipulation of symbolic links within the shared filesystem between guest and host systems. When QEMU processes file operations through VirtFS, it does not adequately verify that symbolic links point to legitimate locations within the designated shared directory structure. This weakness enables a privileged user within the guest operating system to create or manipulate symbolic links that point outside the intended shared folder boundaries. The flaw operates at the filesystem level where the virtualization layer fails to enforce proper path restrictions, allowing arbitrary file system access to the underlying host system.
From an operational perspective, this vulnerability presents a severe threat to virtualized environments where guest operating systems are granted elevated privileges. The impact extends beyond simple data access to potential privilege escalation scenarios where attackers can leverage the flaw to execute arbitrary code on the host system. The vulnerability's severity is compounded by the fact that it requires only a privileged user account within the guest, making it accessible to attackers who have already gained some level of access to the virtual machine. This makes the flaw particularly dangerous in multi-tenant cloud environments or scenarios where guest users might have legitimate administrative access.
The vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and maps to ATT&CK technique T1059 (Command and Scripting Interpreter) and T1068 (Local Privilege Escalation) within the MITRE ATT&CK framework. Organizations using QEMU virtualization platforms are strongly advised to implement immediate mitigations including upgrading to QEMU version 2.9 or later, which contains the necessary patches to address the improper link following behavior. Additional protective measures should include restricting VirtFS functionality where possible, implementing strict access controls on shared directories, and monitoring for suspicious symbolic link creation activities within virtualized environments. The vulnerability demonstrates the critical importance of proper input validation and path resolution in virtualization software, particularly when dealing with shared filesystem operations between guest and host systems.