CVE-2019-11366 in atftp
Summary
by MITRE
An issue was discovered in atftpd in atftp 0.7.1. It does not lock the thread_list_mutex mutex before assigning the current thread data structure. As a result, the daemon is vulnerable to a denial of service attack due to a NULL pointer dereference. If thread_data is NULL when assigned to current, and modified by another thread before a certain tftpd_list.c check, there is a crash when dereferencing current->next.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 09/05/2023
The vulnerability identified as CVE-2019-11366 affects the atftpd daemon version 0.7.1, specifically within the thread management subsystem. This issue represents a classic race condition scenario where concurrent thread operations create unpredictable behavior in the multi-threaded environment. The atftpd service, which provides tftp server functionality for network file transfers, operates with multiple threads handling client requests simultaneously, making proper synchronization mechanisms critical for maintaining service availability and system stability.
The technical flaw manifests in the tftpd_list.c file where the thread_list_mutex mutex is not properly acquired before assigning thread data structures to the current variable. This mutex is designed to protect shared data structures from concurrent access, but its absence during assignment creates a window where multiple threads can interfere with each other's operations. When a thread attempts to assign a thread_data structure to current, another thread may modify or nullify the pointer before the assignment is complete, leading to a scenario where current becomes NULL. The subsequent dereference of current->next in the code path triggers a NULL pointer exception, causing the daemon to crash and terminate its operation.
This vulnerability directly maps to CWE-362, which describes a race condition in concurrent execution environments where multiple threads access shared resources without proper synchronization mechanisms. The flaw represents a classic example of improper locking where the absence of mutex acquisition creates a critical timing window. From an operational perspective, this vulnerability presents a significant denial of service risk as an attacker can repeatedly trigger the race condition to crash the atftpd daemon, effectively preventing legitimate users from accessing network file transfer services. The impact extends beyond simple service disruption as it can affect network infrastructure reliability and availability, particularly in environments where tftp services are critical for boot processes or network management operations.
The attack vector requires minimal privileges and can be executed remotely, making it particularly dangerous in networked environments. The vulnerability demonstrates poor software design practices in concurrent programming where proper mutex usage was omitted during critical sections of code. Mitigation strategies should focus on implementing proper synchronization mechanisms, ensuring that thread_list_mutex is acquired before any assignment operations to thread data structures. Additionally, input validation and proper null pointer checks should be implemented to prevent crashes even when race conditions occur. The fix involves modifying the code to acquire the mutex before assignment operations and ensuring that the thread data structures are properly initialized and validated before dereferencing. Organizations should also consider implementing monitoring systems to detect service disruptions and automated recovery mechanisms to minimize the impact of such vulnerabilities in production environments. This vulnerability highlights the importance of adhering to secure coding practices and proper thread synchronization in multi-threaded applications, as outlined in various security frameworks and best practices for preventing race conditions and related concurrency issues.