CVE-2011-1925 in nbd
Summary
by MITRE
nbd-server.c in Network Block Device (nbd-server) 2.9.21 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) by causing a negotiation failure, as demonstrated by specifying a name for a non-existent export.
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Analysis
by VulDB Data Team • 11/08/2021
The vulnerability identified as CVE-2011-1925 affects the Network Block Device nbd-server version 2.9.21 and represents a critical denial of service flaw that can be exploited remotely by attackers. This issue manifests through a NULL pointer dereference condition that occurs during the negotiation phase of the NBD protocol, specifically when handling requests for non-existent exports. The Network Block Device protocol is designed to allow clients to access block devices over a network connection, making it a critical component in distributed storage environments and virtualization infrastructures. The flaw exists within the nbd-server.c source file where improper error handling leads to the server crashing when encountering malformed or invalid negotiation requests.
The technical exploitation of this vulnerability requires an attacker to initiate a negotiation sequence with the nbd-server while specifying a name for an export that does not exist within the server's configuration. During this negotiation process, the server attempts to process the request and handle the non-existent export scenario, but due to inadequate null pointer checks in the implementation, the program encounters a NULL pointer dereference. This condition causes the nbd-server process to terminate unexpectedly, resulting in a complete denial of service for legitimate users who require access to the network block device services. The vulnerability specifically targets the protocol negotiation phase where the server validates export names and handles client requests, making it particularly dangerous as it can be triggered without authentication or authorization.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect the availability of critical storage services within networked environments. Organizations relying on nbd-server for virtual machine storage, backup operations, or distributed file systems may experience significant downtime when this vulnerability is exploited. The crash condition affects the entire server process, meaning that all active connections and ongoing operations are terminated simultaneously. This makes the vulnerability particularly attractive to attackers seeking to disrupt services without leaving obvious traces, as the crash appears to be a legitimate system failure rather than an intentional attack. The vulnerability also represents a weakness in the server's input validation and error handling mechanisms, indicating broader security issues in the codebase that may be susceptible to additional exploitation vectors.
Mitigation strategies for CVE-2011-1925 should focus on immediate patching of the nbd-server software to version 2.9.22 or later, which contains the necessary fixes for the NULL pointer dereference issue. System administrators should implement network-level access controls to restrict access to nbd-server ports to trusted networks only, reducing the attack surface available to potential remote attackers. Additionally, monitoring systems should be configured to detect unusual patterns of connection attempts or negotiation failures that might indicate exploitation attempts. The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and represents a specific implementation weakness that could be categorized under ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious NBD protocol negotiation sequences, particularly those involving non-existent export names. Regular security audits of network services and proper input validation testing should be conducted to prevent similar issues in other components of the storage infrastructure.