CVE-2013-4535 in QEMU
Summary
by MITRE
The virtqueue_map_sg function in hw/virtio/virtio.c in QEMU before 1.7.2 allows remote attackers to execute arbitrary files via a crafted savevm image, related to virtio-block or virtio-serial read.
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Analysis
by VulDB Data Team • 06/20/2021
The vulnerability identified as CVE-2013-4535 represents a critical security flaw within the QEMU virtualization platform that affects versions prior to 1.7.2. This issue resides in the virtqueue_map_sg function located in the hw/virtio/virtio.c file, which is a fundamental component of QEMU's virtual I/O implementation. The vulnerability specifically impacts virtio-block and virtio-serial devices, which are commonly used virtual hardware components in virtual machine configurations. The flaw enables remote attackers to execute arbitrary code through manipulation of savevm images, which are snapshots of virtual machine states that can be saved and restored. This represents a significant escalation from standard virtualization security boundaries, as it allows attackers to potentially compromise the host system when virtual machines are loaded or restored from maliciously crafted state files.
The technical nature of this vulnerability stems from inadequate input validation and memory handling within the virtqueue mapping mechanism. When a virtual machine is restored from a savevm image, the virtqueue_map_sg function processes scatter-gather lists that describe how data is mapped between virtual and physical memory regions. The flaw occurs when the function fails to properly validate the size and structure of these scatter-gather entries, allowing attackers to craft malicious savevm images that contain oversized or malformed entries. This improper validation creates a buffer overflow condition or memory corruption scenario that can be exploited to redirect execution flow within the QEMU process. The vulnerability is particularly dangerous because it operates at the hypervisor level, where successful exploitation can lead to complete compromise of the host system and all virtual machines running on it. The attack vector is remote since savevm images can be transferred over networks or embedded in malicious files, making it possible for attackers to deliver payloads without requiring local access to the target system.
The operational impact of CVE-2013-4535 extends far beyond individual virtual machine security, affecting entire virtualization infrastructures and cloud computing environments. Organizations that rely on QEMU-based virtualization platforms for hosting multiple tenants or running critical workloads face significant risk, as exploitation can result in privilege escalation, data exfiltration, and persistence mechanisms on the host system. The vulnerability is particularly concerning in multi-tenant environments where virtual machines from different users or organizations are hosted on the same physical infrastructure. Attackers can leverage this flaw to escape virtual machine isolation boundaries, potentially accessing data from other virtual machines or even gaining root access to the underlying host system. The impact is compounded by the fact that savevm images are commonly used for backup, migration, and testing purposes, making the attack surface larger than initially apparent. This vulnerability directly violates the fundamental security principle of virtualization isolation and can be classified under CWE-121 for heap-based buffer overflow conditions. From an attack framework perspective, this vulnerability maps to techniques described in the MITRE ATT&CK framework under the T1059 (Command and Scripting Interpreter) and T1068 (Exploitation for Privilege Escalation) tactics, as it enables arbitrary code execution and privilege escalation within the virtualization environment.
Mitigation strategies for CVE-2013-4535 require immediate action to upgrade QEMU to version 1.7.2 or later, which includes patches addressing the specific validation issues in the virtqueue_map_sg function. Organizations should implement strict access controls and validation for all savevm images, particularly those originating from untrusted sources or networks. Virtualization administrators should disable unnecessary savevm functionality when it is not required for operational purposes, and implement network segmentation to limit exposure to potential attackers. Additional protective measures include regular security audits of virtual machine configurations, implementation of automated scanning tools for malicious savevm images, and maintaining up-to-date virtualization security baselines. The vulnerability highlights the importance of proper input validation and memory management in hypervisor code, reinforcing the need for comprehensive security testing and code review processes for virtualization platforms. Organizations should also consider implementing monitoring solutions that can detect anomalous behavior in virtualization environments, as exploitation attempts may generate unusual memory access patterns or process behavior that can be detected through proper security monitoring. Furthermore, incident response procedures should be updated to include specific handling of hypervisor-level vulnerabilities, ensuring that security teams are prepared to respond to exploitation attempts that could compromise entire virtualization infrastructures.