CVE-2017-16239 in OpenStack
Summary
by MITRE
In OpenStack Nova through 14.0.9, 15.x through 15.0.7, and 16.x through 16.0.2, by rebuilding an instance, an authenticated user may be able to circumvent the Filter Scheduler bypassing imposed filters (for example, the ImagePropertiesFilter or the IsolatedHostsFilter). All setups using Nova Filter Scheduler are affected.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-16239 represents a critical security flaw in OpenStack Nova's scheduling mechanism that affects multiple versions of the cloud infrastructure platform. This issue specifically targets the Filter Scheduler component which is responsible for determining where virtual machine instances should be deployed within a cloud environment. The vulnerability allows authenticated users to exploit a bypass mechanism that undermines the intended filtering controls designed to enforce resource allocation policies and host isolation requirements. The flaw exists in versions prior to 14.0.9, 15.0.7, and 16.0.2, making a significant portion of OpenStack deployments susceptible to this security weakness.
The technical nature of this vulnerability stems from improper validation within the instance rebuilding process within Nova's Filter Scheduler. When users attempt to rebuild an existing instance, the system should maintain the original filtering constraints that were applied during the initial scheduling decision. However, the flaw allows authenticated users to manipulate this process in such a way that the scheduler bypasses critical filters including ImagePropertiesFilter and IsolatedHostsFilter. These filters are designed to enforce specific constraints such as ensuring images meet certain properties or that instances are scheduled on isolated hosts to maintain security boundaries. The bypass mechanism effectively allows malicious users to circumvent these protective measures through legitimate administrative actions.
The operational impact of this vulnerability extends beyond simple privilege escalation as it fundamentally undermines the security architecture of cloud deployments using OpenStack Nova. Organizations that rely on host isolation for security compliance, multi-tenancy separation, or specific resource allocation policies face significant risk when this vulnerability is exploited. Attackers can potentially move instances to hosts that violate established security policies, compromise isolation between tenant environments, or access resources that should be restricted based on image properties or other filtering criteria. This vulnerability particularly affects deployments where security policies are enforced through Nova's scheduling filters, making it a serious concern for cloud administrators who depend on these mechanisms for maintaining secure multi-tenant environments.
The security implications of this vulnerability align with CWE-284 Access Control Issues, specifically targeting inadequate access control mechanisms within the scheduling component of cloud infrastructure. From an adversarial perspective, this flaw maps to ATT&CK technique T1078 Valid Accounts, as it allows authenticated users to leverage their legitimate credentials to bypass security controls. The vulnerability demonstrates a classic case of insufficient input validation and privilege escalation within cloud orchestration systems. Organizations implementing OpenStack Nova should prioritize immediate patching of affected versions, as the bypass affects all setups using the Nova Filter Scheduler regardless of specific configuration. Additionally, administrators should conduct thorough reviews of their scheduling policies and monitor for any unauthorized instance movements that might indicate exploitation attempts.
Mitigation strategies should include immediate deployment of patched Nova versions, comprehensive audit of existing scheduling filters to ensure proper enforcement, and implementation of additional monitoring controls to detect unauthorized instance relocations. Organizations should also consider implementing additional security layers beyond the default Nova filters, such as network segmentation, enhanced logging, and regular security assessments of their cloud infrastructure components. The vulnerability highlights the importance of maintaining up-to-date cloud infrastructure software and the critical need for thorough testing of security controls in multi-tenant environments where isolation requirements are paramount for maintaining security posture.