CVE-2000-0501 in MDaemon
Summary
by MITRE
Race condition in MDaemon 2.8.5.0 POP server allows local users to cause a denial of service by entering a UIDL command and quickly exiting the server.
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Analysis
by VulDB Data Team • 10/14/2025
The vulnerability described in CVE-2000-0501 represents a classic race condition flaw within the MDaemon 2.8.5.0 POP server implementation that exposes a critical weakness in the server's handling of mailbox access operations. This race condition specifically manifests during the processing of UIDL commands, which are used to retrieve unique identifiers for messages in a mailbox. The flaw occurs when a local user rapidly executes the UIDL command followed by an immediate disconnection from the server, creating a temporal window where the server's internal state management becomes inconsistent.
The technical root cause of this vulnerability stems from inadequate synchronization mechanisms within the MDaemon POP server's message handling architecture. When a UIDL command is processed, the server typically retrieves message identifiers and prepares them for transmission to the client. However, the race condition occurs because the server does not properly manage the state transition between command processing and connection termination. This lack of proper state management allows a malicious user to exploit the temporal gap between when the UIDL command is initiated and when the connection is fully closed, resulting in a scenario where the server's internal data structures become corrupted or left in an inconsistent state.
From an operational impact perspective, this vulnerability enables local users to trigger a denial of service condition that effectively disrupts legitimate mail services. The attack is particularly concerning because it requires minimal privileges and can be executed with simple command sequences, making it accessible to any user with local access to the system. The DoS condition manifests as the server becoming unresponsive or crashing, which prevents legitimate users from accessing their email accounts and can potentially impact the entire mail service availability for all users on the affected system. This vulnerability directly maps to CWE-362, which describes race conditions in software systems, and aligns with ATT&CK technique T1499.004 for network denial of service attacks.
The exploitation of this vulnerability demonstrates how seemingly innocuous protocol commands can become weaponized when server implementations lack proper concurrency controls. The rapid execution sequence of UIDL command followed by immediate exit creates a timing scenario where the server's cleanup routines and state management routines do not properly synchronize with the command processing flow. This type of vulnerability is particularly dangerous in email server environments where service availability is critical for business operations and communication continuity. The impact extends beyond simple service disruption as it can potentially lead to data corruption or loss if the server state becomes irreparably compromised during the race condition window.
Mitigation strategies for this vulnerability should focus on implementing proper synchronization mechanisms within the server's command processing pipeline and ensuring that all state transitions are properly managed during connection lifecycle events. System administrators should consider applying the vendor-provided patches or upgrading to newer versions of MDaemon that address this race condition. Additionally, implementing monitoring solutions that can detect unusual patterns of UIDL command execution followed by rapid disconnections can help identify potential exploitation attempts. The vulnerability highlights the importance of proper concurrent programming practices and the need for thorough testing of server implementations under various timing conditions to prevent similar race condition scenarios from occurring in other components of the email infrastructure.