CVE-2019-3886 in libvirt
Summary
by MITRE
An incorrect permissions check was discovered in libvirt 4.8.0 and above. The readonly permission was allowed to invoke APIs depending on the guest agent, which could lead to potentially disclosing unintended information or denial of service by causing libvirt to block.
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Analysis
by VulDB Data Team • 08/27/2023
The vulnerability identified as CVE-2019-3886 represents a critical permission escalation flaw within the libvirt virtualization management framework. This issue affects libvirt versions 4.8.0 and later, where an improper access control mechanism allows users with read-only permissions to execute privileged APIs that should typically be restricted to administrators or users with elevated privileges. The flaw specifically manifests when read-only users attempt to invoke guest agent dependent APIs, creating an unexpected pathway for privilege abuse that undermines the fundamental security model of the virtualization environment.
The technical implementation of this vulnerability stems from inadequate validation of user permissions within the libvirt daemon's API handling mechanisms. When a read-only user attempts to interact with guest agent functionality, the system fails to properly enforce the distinction between read-only and administrative privileges. This misconfiguration allows the execution of operations that could potentially expose sensitive information about guest operating systems, virtual machine configurations, or underlying host resources. The vulnerability operates at the API level within libvirt's permission system, where the access control lists do not adequately differentiate between read-only operations and those requiring elevated privileges.
The operational impact of CVE-2019-3886 extends beyond simple information disclosure to encompass potential denial of service conditions that can severely disrupt virtualization environments. Attackers with read-only access can leverage this vulnerability to cause libvirt daemon instability, potentially leading to service interruptions that affect multiple virtual machines managed by the same hypervisor. The ability to trigger denial of service conditions through guest agent APIs represents a significant escalation risk, as it allows unprivileged users to impact the availability of critical virtualization services. Additionally, the information disclosure aspect could reveal sensitive configuration details that might aid in further attacks against the virtualized infrastructure.
This vulnerability aligns with CWE-284, which describes improper access control mechanisms in software systems. The flaw demonstrates a classic case of insufficient privilege checking where the system fails to properly validate user credentials against the required security context for specific operations. From an adversarial perspective, this vulnerability maps to several ATT&CK techniques including privilege escalation and defense evasion, as attackers can leverage the misconfigured permissions to gain unauthorized access to sensitive data and potentially disrupt system operations. The attack surface is particularly concerning in multi-tenant virtualization environments where different users share the same hypervisor infrastructure, as a single compromised read-only account could potentially impact the entire virtualization platform.
Mitigation strategies for CVE-2019-3886 should focus on immediate patching of affected libvirt installations to versions that properly address the permission validation flaw. Organizations should also implement additional monitoring of API access patterns to detect anomalous behavior that might indicate exploitation attempts. Network segmentation and least privilege principles should be enforced to limit the potential impact of compromised accounts, while regular security audits of virtualization management interfaces can help identify similar permission misconfigurations. The vulnerability highlights the importance of comprehensive access control testing and validation, particularly for complex systems like libvirt that manage critical virtualization infrastructure components and require robust permission enforcement mechanisms to maintain security boundaries between different user roles and operational contexts.