CVE-2019-14850 in nbdkit
Summary
by MITRE • 03/19/2021
A denial of service vulnerability was discovered in nbdkit 1.12.7, 1.14.1 and 1.15.1. An attacker could connect to the nbdkit service and cause it to perform a large amount of work in initializing backend plugins, by simply opening a connection to the service. This vulnerability could cause resource consumption and degradation of service in nbdkit, depending on the plugins configured on the server-side.
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Analysis
by VulDB Data Team • 04/02/2021
The vulnerability identified as CVE-2019-14850 represents a significant denial of service weakness in the nbdkit service, a widely used network block device server that facilitates virtual machine disk image management across various cloud and virtualization environments. This flaw affects specific versions including 1.12.7, 1.14.1, and 1.15.1, making it a persistent threat across multiple release branches of the software. The vulnerability stems from insufficient input validation and resource management during the connection initialization phase, where the service fails to properly limit or monitor the computational overhead required for backend plugin initialization. This weakness allows malicious actors to exploit the service through simple connection attempts without requiring complex attack vectors or elevated privileges, making it particularly dangerous in production environments where nbdkit serves critical virtualization infrastructure.
The technical implementation of this vulnerability exploits the inherent design pattern where nbdkit must initialize backend plugins upon connection establishment to determine available storage devices and their properties. When an attacker establishes a connection, the service automatically triggers the initialization process for all configured plugins, regardless of whether the connection will ultimately be used for data operations. This initialization process can involve extensive resource consumption including memory allocation, file system operations, network requests, and CPU intensive computations depending on the specific plugins configured. The flaw lies in the absence of rate limiting or resource consumption monitoring during the plugin initialization phase, allowing an attacker to repeatedly open connections and cause the service to perform disproportionate amounts of work relative to the actual utility of each connection attempt. This behavior manifests as resource exhaustion and service degradation rather than complete system failure, making it particularly insidious as it can remain undetected while gradually degrading system performance.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader infrastructure reliability concerns within virtualization and cloud computing environments. Organizations relying on nbdkit for managing virtual machine disk images, backup operations, and storage provisioning face potential service degradation that could affect multiple virtual machines simultaneously. The vulnerability particularly impacts systems where multiple backend plugins are configured, as each connection attempt triggers initialization of all plugins, potentially creating cascading resource consumption effects. Attackers can leverage this weakness to perform sustained resource exhaustion attacks that may persistently degrade service quality without requiring sophisticated techniques or privileged access. The vulnerability's implications are further amplified in multi-tenant environments where a single compromised connection could affect service availability for multiple users or applications relying on the same nbdkit instance. This weakness directly violates security principles related to resource management and input validation, creating opportunities for attackers to consume excessive computational resources and potentially cause denial of service conditions that affect business-critical operations.
Mitigation strategies for CVE-2019-14850 should focus on both immediate patching and operational hardening measures to address the root cause of the vulnerability. The primary remediation involves upgrading to nbdkit versions that contain fixes for this specific issue, typically found in versions released after the vulnerability disclosure. Organizations should implement connection rate limiting at the network level to prevent rapid connection flooding that could trigger the resource exhaustion behavior. Additionally, administrators should review and minimize the number of backend plugins configured on nbdkit instances, as each plugin contributes to the computational overhead during connection initialization. Network segmentation and access control measures can help limit exposure by restricting which systems can establish connections to nbdkit services. The vulnerability aligns with CWE-400, which addresses unrestricted resource consumption, and may be relevant to ATT&CK techniques related to resource exhaustion and denial of service. Monitoring and alerting should be implemented to detect unusual connection patterns or resource consumption spikes that could indicate exploitation attempts. Regular security audits of virtualization infrastructure should include assessment of nbdkit configurations to ensure proper resource management and prevent similar vulnerabilities from emerging in other components of the virtualization stack.