CVE-2015-0268 in Xen
Summary
by MITRE
The vgic_v2_to_sgi function in arch/arm/vgic-v2.c in Xen 4.5.x, when running on ARM hardware with general interrupt controller (GIC) version 2, allows local guest users to cause a denial of service (host crash) by writing an invalid value to the GICD.SGIR register.
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Analysis
by VulDB Data Team • 03/10/2022
The vulnerability identified as CVE-2015-0268 represents a critical denial of service flaw within the Xen hypervisor's virtual GIC implementation, specifically affecting versions 4.5.x when operating on ARM hardware with GICv2. This issue stems from inadequate input validation within the vgic_v2_to_sgi function located in arch/arm/vgic-v2.c, which handles the translation of software-generated interrupts from virtualized guests to the underlying physical interrupt controller. The flaw occurs when guest operating systems attempt to write invalid values to the GICD.SGIR register, a mechanism designed for generating software interrupts within the GIC architecture. The vulnerability exploits the lack of proper bounds checking and validation of interrupt identifiers, allowing malicious or compromised guest users to craft malformed interrupt requests that bypass normal safety mechanisms. This specific weakness falls under CWE-129, Input Validation, and more specifically addresses improper validation of input parameters within interrupt handling code. The ATT&CK framework categorizes this as a privilege escalation technique through hypervisor manipulation, as guest users can leverage this vulnerability to affect the stability and operation of the host system.
The technical exploitation of CVE-2015-0268 requires a guest user to manipulate the GICD.SGIR register with values that the hypervisor's vgic_v2_to_sgi function does not properly validate. When such invalid values are written to this register, the function fails to handle the malformed input correctly, leading to undefined behavior that can result in kernel crashes or system instability. The GICv2 register structure defines specific bit layouts and valid ranges for interrupt identifiers, but the Xen implementation fails to validate these constraints before processing the interrupt request. This creates a path where untrusted guest input can directly influence the hypervisor's kernel execution flow, potentially causing memory corruption or invalid memory access patterns that trigger system crashes. The vulnerability is particularly dangerous because it operates at the hypervisor level, where guest users typically have limited privileges but can still cause host-level disruptions. The impact extends beyond simple service interruption as the host crash can affect all virtual machines running on that hypervisor instance, potentially leading to cascading failures in virtualized environments.
The operational consequences of CVE-2015-0268 are significant for organizations relying on Xen virtualization platforms, particularly those utilizing ARM-based hardware. A successful exploitation can result in complete system downtime, requiring manual intervention to restart affected hypervisor instances and potentially leading to data loss or service interruptions for multiple virtualized applications. The vulnerability is especially concerning in cloud computing environments where multiple tenants share the same hypervisor infrastructure, as a malicious guest user could potentially disrupt services for other virtual machines on the same host. Network infrastructure providers and service offerings built on Xen virtualization are particularly vulnerable, as this flaw could be exploited to create denial of service conditions affecting network connectivity or application availability. Organizations running virtualized environments on ARM hardware with Xen 4.5.x are at risk of experiencing operational disruptions that could impact business continuity and service level agreements. The vulnerability also represents a potential attack vector for advanced persistent threats that might leverage such flaws to gain further control over virtualized systems.
Mitigation strategies for CVE-2015-0268 primarily involve immediate patching of affected Xen hypervisor versions, with the recommended solution being an upgrade to Xen 4.5.1 or later versions that contain the appropriate fixes for the vgic_v2_to_sgi function. System administrators should also implement monitoring solutions to detect anomalous patterns in GIC register access that might indicate attempted exploitation of this vulnerability. Additional defensive measures include restricting guest privileges where possible, implementing proper input validation at multiple levels, and ensuring that virtual machine configurations do not allow unnecessary access to GIC registers. Network segmentation and hypervisor hardening practices should be employed to limit the potential impact of such vulnerabilities. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates. The fix for this vulnerability typically involves adding proper validation checks within the vgic_v2_to_sgi function to verify that interrupt identifiers fall within acceptable ranges before processing them, thereby preventing invalid values from causing system crashes. Compliance with industry standards such as NIST SP 800-53 and ISO 27001 requires organizations to maintain up-to-date hypervisor implementations and to conduct regular vulnerability assessments to identify and remediate similar security flaws in virtualization environments.