CVE-2009-2906 in Samba
Summary
by MITRE
smbd in Samba 3.0 before 3.0.37, 3.2 before 3.2.15, 3.3 before 3.3.8, and 3.4 before 3.4.2 allows remote authenticated users to cause a denial of service (infinite loop) via an unanticipated oplock break notification reply packet.
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Analysis
by VulDB Data Team • 01/25/2025
The vulnerability identified as CVE-2009-2906 represents a critical denial of service flaw affecting Samba implementations across multiple version branches. This issue specifically targets the smbd daemon which serves as the primary file sharing service in Samba environments. The vulnerability manifests when authenticated remote users can trigger an infinite loop condition through the manipulation of oplock break notification reply packets, effectively causing the targeted Samba service to become unresponsive and consume excessive system resources. The flaw exists within the oplock handling mechanism that manages opportunistic locking operations between client and server during file access scenarios.
The technical root cause of this vulnerability lies in the improper handling of oplock break notifications within the Samba server implementation. When a client requests an oplock break from the server, the server responds with a specific packet format containing oplock break information. However, the vulnerable versions fail to properly validate or process certain reply packets that may contain unexpected oplock break notification data. This processing error creates a condition where the server enters an infinite loop while attempting to handle the malformed packet, resulting in continuous resource consumption and eventual system unresponsiveness. The vulnerability specifically affects the oplock break handling code path in the smbd daemon, which is responsible for managing file locking operations in networked file systems.
From an operational perspective, this vulnerability presents significant risks to organizations relying on Samba file sharing services. The denial of service condition can be triggered by authenticated users who have legitimate access to the Samba server, making it particularly dangerous in environments where user access controls are not strictly enforced. The infinite loop consumes CPU resources and can potentially affect other services running on the same system. Network administrators may observe increased system load, unresponsive file sharing services, and potential cascading effects on dependent applications. The vulnerability's impact is amplified because it requires only authenticated access, meaning that users with valid credentials can exploit it without requiring special privileges or advanced technical knowledge.
The security implications extend beyond simple service disruption, as this vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under the technique of denial of service. Organizations may find their file sharing infrastructure compromised, leading to productivity losses and potential business continuity issues. The vulnerability also represents a weakness in the Samba software's input validation mechanisms, which should properly handle all expected and unexpected packet formats. According to CWE classification, this vulnerability maps to CWE-121, which describes stack-based buffer overflow conditions that can lead to denial of service scenarios through infinite loops or other resource exhaustion techniques. Organizations should prioritize immediate patching of affected Samba versions, particularly those in the 3.0.x, 3.2.x, 3.3.x, and 3.4.x release branches. Additionally, implementing network monitoring to detect unusual oplock break notification patterns and establishing robust access control measures can help mitigate potential exploitation attempts. The recommended mitigation strategy includes applying the latest security patches from the Samba project, which address the improper oplock break handling logic and implement proper validation of incoming notification packets to prevent the infinite loop condition from occurring.