CVE-2011-2527 in Qemu
Summary
by MITRE
The change_process_uid function in os-posix.c in Qemu 0.14.0 and earlier does not properly drop group privileges when the -runas option is used, which allows local guest users to access restricted files on the host.
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Analysis
by VulDB Data Team • 01/12/2025
The vulnerability described in CVE-2011-2527 represents a critical privilege escalation flaw within the QEMU virtualization platform that affects versions 0.14.0 and earlier. This issue stems from improper privilege management during the virtual machine execution process, specifically within the os-posix.c file where the change_process_uid function fails to correctly drop group privileges when the -runas option is employed. The flaw creates a dangerous condition where local users within a guest operating system can potentially access files and resources on the host system that should normally be restricted. This vulnerability directly impacts the fundamental security boundary between virtual machines and their host environments, undermining the isolation that virtualization platforms are designed to provide.
The technical implementation of this vulnerability involves the change_process_uid function in QEMU's POSIX operating system support code, which is responsible for managing user and group identity changes when virtual machines are started with specific user privileges. When administrators utilize the -runas option to specify a particular user context for QEMU processes, the system should properly transition from elevated privileges to the specified user context while also dropping any unnecessary group memberships. However, the flaw in the implementation means that group privileges are not adequately stripped, leaving the process with elevated group permissions that persist beyond the intended scope. This creates a pathway for privilege escalation where guest users can leverage these retained group memberships to access host resources that are protected by group-based access controls.
The operational impact of this vulnerability extends beyond simple file access and represents a significant threat to host system integrity and security. Local guest users can exploit this flaw to read sensitive files, access restricted system resources, and potentially execute arbitrary code with elevated privileges on the host system. The vulnerability particularly affects environments where QEMU is used with the -runas option, which is common in cloud computing and virtualization deployments where security isolation is paramount. Attackers could use this vulnerability to extract confidential data, establish persistence mechanisms, or escalate privileges to gain full control over the host system. The implications are severe because virtualization environments often contain sensitive data and critical system components that should remain isolated from guest operating systems.
From a cybersecurity perspective, this vulnerability maps directly to CWE-276, which describes improper privileges, and aligns with several ATT&CK techniques including privilege escalation and credential access. The flaw demonstrates poor privilege management practices and highlights the importance of proper security context handling in virtualization software. Organizations using affected QEMU versions should immediately implement mitigations including upgrading to patched versions where available, reviewing and restricting the use of the -runas option, and implementing additional host-level security controls. The vulnerability also underscores the necessity of comprehensive privilege management testing in virtualization platforms and the critical need for proper privilege separation between host and guest environments to maintain the security guarantees that virtualization technologies are designed to provide.
This vulnerability serves as a stark reminder of the complex security considerations inherent in virtualization environments where multiple security contexts must be properly managed. The failure to correctly drop group privileges represents a fundamental flaw in the privilege management architecture and demonstrates how seemingly small implementation details can create significant security risks. System administrators and security professionals should prioritize updating affected QEMU installations and conducting thorough security assessments of their virtualization environments to identify and remediate similar privilege management issues. The incident also highlights the importance of proper security testing for virtualization platforms and the need for comprehensive security controls that address both host and guest security boundaries to prevent unauthorized access and privilege escalation attacks.