CVE-2012-3515 in XenServer
Summary
by MITRE
Qemu, as used in Xen 4.0, 4.1 and possibly other products, when emulating certain devices with a virtual console backend, allows local OS guest users to gain privileges via a crafted escape VT100 sequence that triggers the overwrite of a "device model s address space."
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Analysis
by VulDB Data Team • 07/23/2018
The vulnerability identified as CVE-2012-3515 represents a critical privilege escalation flaw within the Qemu emulation layer that was integrated into Xen hypervisor versions 4.0 and 4.1. This issue specifically affects virtualized environments where guest operating systems run within Xen virtual machines and utilize Qemu for device emulation. The vulnerability stems from inadequate input validation within the VT100 terminal sequence processing mechanism that Qemu employs when handling virtual console backends. When a malicious guest user executes a crafted VT100 escape sequence, the system fails to properly sanitize or validate the sequence parameters, leading to a buffer overflow condition in the device model's address space. This flaw falls under the CWE-121 category of stack-based buffer overflow, though it manifests in a more complex virtualization context where the attack surface extends beyond traditional operating system boundaries. The vulnerability is particularly dangerous because it operates at the hypervisor level, allowing guest users to potentially compromise the entire virtualized environment.
The technical exploitation of this vulnerability involves the construction of a specific VT100 escape sequence that when processed by the emulated console device, causes memory corruption in the device model's memory space. The device model in Xen operates with elevated privileges to manage virtual hardware resources, and when the crafted sequence triggers an overwrite of this address space, it can lead to arbitrary code execution within the hypervisor context. This type of attack aligns with ATT&CK technique T1055 which covers process injection and privilege escalation techniques. The vulnerability is particularly concerning because the attack can be executed by any local user within the guest operating system, requiring no network access or external attack vectors. The memory corruption occurs due to improper bounds checking in the VT100 sequence parser, which fails to validate the length and parameters of escape sequences before attempting to process them within the device model's memory regions.
The operational impact of CVE-2012-3515 extends far beyond individual virtual machine compromise, as successful exploitation can lead to complete hypervisor compromise and subsequent access to all virtual machines hosted on the same physical system. An attacker who successfully exploits this vulnerability can potentially gain root privileges within the hypervisor, allowing them to manipulate or steal data from all VMs running on the affected host. This represents a severe multi-tenant security breach in virtualized environments where isolation between guests is expected. The vulnerability affects organizations using Xen hypervisors in cloud computing environments, virtual desktop infrastructures, and any deployment where multiple users share the same physical hardware through virtualization. The impact is particularly severe in enterprise environments where virtualization is used extensively for resource optimization and security isolation, as this vulnerability undermines the fundamental security model of virtualization. Organizations may experience data breaches, service disruptions, and potential compliance violations when this vulnerability is exploited in production environments.
Mitigation strategies for CVE-2012-3515 require immediate patching of affected Xen hypervisor versions, with the most effective solution being the upgrade to Xen 4.2 or later versions that contain the necessary fixes for the VT100 sequence processing vulnerability. System administrators should also implement network segmentation and access controls to limit guest user privileges and reduce the attack surface. Additional protective measures include disabling unnecessary virtual device emulations, monitoring for unusual VT100 sequence patterns in console logs, and implementing hypervisor-level security monitoring. The vulnerability highlights the importance of input validation in virtualization components and the need for comprehensive security testing of hypervisor code. Organizations should also consider implementing micro-segmentation policies and privilege separation between guest operating systems and hypervisor components to limit the potential impact of similar vulnerabilities. Regular security audits of virtualization environments and maintaining updated security patches are essential practices to prevent exploitation of this and similar vulnerabilities.