CVE-2014-0146 in QEMU
Summary
by MITRE
The qcow2_open function in the (block/qcow2.c) in QEMU before 1.7.2 and 2.x before 2.0.0 allows local users to cause a denial of service (NULL pointer dereference) via a crafted image which causes an error, related to the initialization of the snapshot_offset and nb_snapshots fields.
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Analysis
by VulDB Data Team • 06/16/2021
The qcow2_open function vulnerability in QEMU represents a critical denial of service weakness that emerged in virtualization environments leveraging the QEMU emulator. This flaw affects versions prior to 1.7.2 and 2.x versions before 2.0.0, creating a scenario where maliciously crafted image files can trigger a NULL pointer dereference condition during the initialization phase of qcow2 storage format handling. The vulnerability specifically targets the improper handling of snapshot_offset and nb_snapshots fields, which are fundamental components in the qcow2 disk image structure that manage snapshot metadata and tracking information.
The technical execution of this vulnerability occurs when a local attacker presents a specially crafted qcow2 image file to the QEMU hypervisor during the qcow2_open function execution. During the image initialization process, the function attempts to process snapshot-related metadata fields without proper validation of their initialization state. When the snapshot_offset and nb_snapshots fields remain uninitialized or improperly set, subsequent operations within the qcow2_open function lead to a NULL pointer dereference, causing the virtual machine process to crash and resulting in a denial of service condition. This represents a classic case of insufficient input validation and error handling within the storage subsystem of the virtualization platform.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited in environments where QEMU serves as the underlying virtualization engine for cloud computing platforms, containerized applications, or desktop virtualization solutions. Attackers can leverage this weakness to repeatedly crash virtual machine instances, potentially leading to availability issues for critical workloads or disrupting service continuity in cloud infrastructure environments. The vulnerability's local nature means that exploitation requires access to the host system or guest environment where QEMU is running, making it particularly concerning in multi-tenant cloud deployments where isolation between virtual machines is paramount.
This vulnerability maps directly to CWE-476, which identifies NULL pointer dereference as a fundamental weakness in software development practices. The flaw demonstrates inadequate error handling and resource management in the qcow2 block driver implementation, where proper initialization checks should have been implemented before accessing potentially uninitialized memory locations. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.001, which encompasses network denial of service attacks through exploitation of software vulnerabilities. The attack chain typically involves preparing a malicious qcow2 image file, presenting it to a vulnerable QEMU instance, and observing the resulting crash or system instability. Mitigation strategies should include immediate patching of affected QEMU versions to 1.7.2 or later, implementing proper input validation for disk image files, and establishing monitoring systems to detect unusual crash patterns in virtualization environments. Additionally, organizations should consider implementing network segmentation and access controls to limit local file system access to QEMU processes, reducing the attack surface for potential exploitation of this and similar vulnerabilities.