By Splunk May 14, 2015
VENOM Vulnerability Disclosure – CVE-2015-3456
A new vulnerability called VENOM, Virtualized Environment Neglected Operations Manipulation, has been discovered (CVE-2015-3456).
What is the vulnerability (per Crowdstrike)?
“The guest operating system communicates with the FDC by sending commands such as seek, read, write, format, etc. to the FDC’s input/output port. QEMU’s virtual FDC uses a fixed-size buffer for storing these commands and their associated data parameters. The FDC keeps track of how much data to expect for each command and, after all expected data for a given command is received from the guest system, the FDC executes the command and clears the buffer for the next command. This buffer reset is performed immediately at the completion of processing for all FDC commands, except for two of the defined commands. An attacker can send these commands and specially crafted parameter data from the guest system to the FDC to overflow the data buffer and execute arbitrary code in the context of the host’s hypervisor process.”
The reach and risk level of this vulnerability can be visualized in the relationship between the hypervisor (host) and the guest (virtual machine). It is possible, through this type of vulnerability, to bypass the protection rings of the virtualization architecture.
Basically, this vulnerability would allow an attacker craft malicious code against two specific commands used to communicate with the floppy disc controller (FDC) of the VM where a buffer reset is not performed thereby allowing overflow of the data buffer and execute code on the host, effectively escaping hypervisor (host) limitations. This also opens the possibility of pivoting or lateral movement against peers or co-tenants in cloud environments (PAAS, IAAS).