CVE-2007-1366 in QEMU
Summary
by MITRE
QEMU 0.8.2 allows local users to crash a virtual machine via the divisor operand to the aam instruction, as demonstrated by "aam 0x0," which triggers a divide-by-zero error.
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Analysis
by VulDB Data Team • 08/30/2018
The vulnerability identified as CVE-2007-1366 resides within QEMU version 0.8.2, a widely used open-source machine emulator and virtualization solution that enables the execution of operating systems and applications in virtual environments. This particular flaw represents a critical issue in the processor emulation layer where the virtual machine monitor fails to properly handle specific x86 instruction operands. The vulnerability specifically targets the aam (ASCII Adjust After Multiply) instruction, which is designed to convert the result of a multiplication operation into unpacked binary-coded decimal format. When a local user executes the malicious instruction "aam 0x0" within a virtual machine environment, the system encounters a divide-by-zero error condition that ultimately leads to a virtual machine crash.
The technical exploitation of this vulnerability occurs through the improper handling of the divisor operand within the aam instruction implementation. In standard x86 processor execution, the aam instruction takes a single operand that specifies the base for the adjustment operation, typically set to 10 for decimal adjustment or 16 for hexadecimal adjustment. When the operand is set to zero, as demonstrated in the exploit, the instruction attempts to perform a division operation by zero, which causes a processor exception that is not properly caught or handled by the QEMU emulation layer. This failure in exception handling results in an uncontrolled termination of the virtual machine process, effectively creating a denial-of-service condition that can be reliably triggered by any local user with access to the virtual machine environment.
The operational impact of CVE-2007-1366 extends beyond simple service disruption to encompass potential security implications within virtualized environments. Since the vulnerability can be exploited by local users who already have access to the virtual machine, it represents a privilege escalation vector that could potentially be leveraged by attackers to gain additional control over the host system or other virtual machines running on the same host. This vulnerability aligns with CWE-129, which addresses improper handling of exceptional conditions, and specifically relates to the improper handling of division by zero errors in processor emulation contexts. The flaw demonstrates a fundamental weakness in the input validation and error handling mechanisms within the virtual machine's processor emulator, where user-provided instruction operands are not adequately sanitized before being processed.
From a cybersecurity perspective, this vulnerability exemplifies the challenges inherent in virtualization security and the importance of comprehensive testing for virtual machine monitors. The ATT&CK framework categorizes this type of vulnerability under the T1499.004 technique related to Virtualization/Sandbox Evasion, as it exploits the trust boundary between the virtual machine and the host system through improper emulation of processor instructions. Organizations relying on QEMU for virtualization deployments would be particularly vulnerable to this type of attack, as it allows for arbitrary code execution within the virtual environment that can lead to complete system compromise. The vulnerability also highlights the need for proper input validation and exception handling in virtualization software, as outlined in various security standards including ISO/IEC 27001 and NIST SP 800-144. Mitigation strategies should include immediate patching of QEMU to version 0.8.3 or later, where the vulnerability has been addressed through proper exception handling for invalid divisor operands. Additionally, implementing strict virtual machine access controls and monitoring for anomalous instruction sequences can help detect and prevent exploitation attempts. System administrators should also consider deploying intrusion detection systems that can identify suspicious patterns in virtual machine execution and maintain comprehensive backup and recovery procedures to address potential service disruptions caused by this vulnerability.