CVE-2004-0794 in NetBSD
Summary
by MITRE
Multiple signal handler race conditions in lukemftpd (aka tnftpd before 20040810) allow remote authenticated attackers to cause a denial of service or execute arbitrary code.
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Analysis
by VulDB Data Team • 06/29/2019
The vulnerability identified as CVE-2004-0794 resides within the lukemftpd implementation commonly known as tnftpd, a network file transfer protocol daemon that was widely deployed in Unix-like operating systems. This particular flaw manifests as multiple signal handler race conditions that occur during the processing of network requests, creating a dangerous window where concurrent operations can lead to unpredictable behavior. The vulnerability affects versions of tnftpd prior to the 20040810 release, indicating that this was a well-known issue that required immediate attention from system administrators and security teams. These race conditions specifically involve the interaction between signal handling mechanisms and the daemon's processing of incoming network connections, creating opportunities for malicious actors to exploit the timing-sensitive nature of these operations.
The technical flaw stems from improper synchronization mechanisms within the signal handling code that governs how the daemon responds to various interrupt signals during file transfer operations. When multiple signals arrive simultaneously or when signal handlers are invoked during critical sections of code execution, the race conditions can cause the daemon to enter an inconsistent state. This inconsistency can manifest in several ways including memory corruption, improper resource management, or execution flow disruption. The vulnerability is particularly dangerous because it allows authenticated remote attackers to leverage these race conditions for either denial of service attacks that can crash the service or more severe exploitation that can lead to arbitrary code execution within the context of the running daemon process.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a critical security flaw that can be exploited by adversaries with network access and valid credentials to compromise system integrity. When exploited successfully, attackers can cause the ftp daemon to crash repeatedly, leading to denial of service for legitimate users and potentially allowing for privilege escalation if the daemon runs with elevated privileges. The race conditions are particularly challenging to exploit reliably due to their timing-dependent nature, but the fact that they can be triggered through normal authenticated operations makes them particularly concerning for production environments. This vulnerability directly relates to CWE-362, which describes race conditions in software systems, and aligns with ATT&CK technique T1068, which covers exploitation of remote services.
Mitigation strategies for CVE-2004-0794 require immediate patching of affected systems with the corrected tnftpd version released after 20040810, which addressed the signal handling race conditions through proper synchronization mechanisms. System administrators should also implement network segmentation and access controls to limit the exposure of vulnerable ftp services to untrusted networks. Additional defensive measures include monitoring for unusual connection patterns or service disruptions that might indicate exploitation attempts, implementing intrusion detection systems that can detect anomalous behavior in ftp daemon processes, and ensuring that ftp services run with minimal required privileges to limit potential damage from successful exploitation. Organizations should also consider migrating to more modern and actively maintained ftp implementations that have better security track records and more robust handling of concurrent operations and signal processing.