CVE-2015-3456 in QEMU
Summary
by MITRE
The Floppy Disk Controller (FDC) in QEMU, as used in Xen 4.5.x and earlier and KVM, allows local guest users to cause a denial of service (out-of-bounds write and guest crash) or possibly execute arbitrary code via the (1) FD_CMD_READ_ID, (2) FD_CMD_DRIVE_SPECIFICATION_COMMAND, or other unspecified commands, aka VENOM.
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Analysis
by VulDB Data Team • 12/21/2024
The vulnerability identified as CVE-2015-3456 represents a critical security flaw in the Floppy Disk Controller implementation within QEMU virtualization software. This issue affects multiple virtualization platforms including Xen 4.5.x and earlier versions as well as KVM hypervisors, making it a widespread concern across virtualized environments. The vulnerability stems from improper input validation and memory handling within the FDC subsystem, which processes various floppy disk commands that guest operating systems can send to the virtual floppy controller.
The technical exploitation of this vulnerability occurs through specific floppy disk controller commands including FD_CMD_READ_ID and FD_CMD_DRIVE_SPECIFICATION_COMMAND, along with other unspecified commands that share similar memory access patterns. When these commands are processed by the vulnerable QEMU implementation, they trigger out-of-bounds write operations that can corrupt memory regions beyond the intended buffer boundaries. This memory corruption can lead to unpredictable behavior including guest operating system crashes or potentially allow privilege escalation to the host system. The vulnerability is particularly dangerous because it can be triggered by unprivileged guest users who have access to floppy disk emulation functionality, making it exploitable in multi-tenant virtualized environments.
The operational impact of CVE-2015-3456 extends beyond simple denial of service conditions to potentially enable arbitrary code execution within the host system. This represents a significant escalation from a simple DoS attack to a full compromise of the virtualization infrastructure. The vulnerability affects the fundamental security model of virtualization by allowing guest users to escape their isolated environment and potentially gain access to host resources. This aligns with ATT&CK technique T1083 for discovering host file systems and T1059 for command and scripting interpreter usage, as the vulnerability enables malicious actors to execute commands within the host environment.
From a CWE perspective, this vulnerability maps to CWE-787 Out-of-bounds Write, which occurs when a program writes data past the end of a buffer. The issue also relates to CWE-121 Stack-based Buffer Overflow and CWE-122 Heap-based Buffer Overflow, depending on the specific memory access patterns during exploitation. The vulnerability demonstrates how virtualization layer components can introduce security risks that affect the entire host infrastructure, particularly when handling user-supplied data through emulated hardware devices. The VENOM vulnerability name reflects the severity and potential for exploitation through the virtualized environment.
Mitigation strategies for CVE-2015-3456 require immediate patching of affected QEMU versions and virtualization platforms. System administrators should disable floppy disk emulation in virtual machines where this functionality is not required, as a temporary workaround. The vulnerability highlights the importance of thorough input validation and memory safety practices in virtualization software components. Organizations should also implement monitoring for unusual memory access patterns and ensure that virtualization environments are regularly updated to address known vulnerabilities. The incident underscores the need for comprehensive security testing of virtualization components and proper sandboxing of guest operating systems to prevent escape from isolated environments.