CVE-2019-18178 in FreeRTOS
Summary
by MITRE
Real Time Engineers FreeRTOS+FAT 160919a has a use after free. The function FF_Close() is defined in ff_file.c. The file handler pxFile is freed by ffconfigFREE, which (by default) is a macro definition of vPortFree(), but it is reused to flush modified file content from the cache to disk by the function FF_FlushCache().
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Analysis
by VulDB Data Team • 11/05/2019
The vulnerability identified as CVE-2019-18178 resides within the Real Time Engineers FreeRTOS+FAT library version 160919a, representing a critical use-after-free condition that fundamentally compromises the integrity of file system operations. This flaw manifests in the FF_Close() function located within the ff_file.c source file, where a file handler structure pxFile undergoes deallocation through the ffconfigFREE macro, which defaults to vPortFree() implementation. The severity of this issue stems from the fact that the same memory location referenced by pxFile continues to be utilized in subsequent operations, specifically within the FF_FlushCache() function that attempts to flush modified file content from cache to disk. The operational context of this vulnerability becomes particularly dangerous in embedded systems environments where FreeRTOS+FAT serves as a foundational component for file management, as it creates potential attack vectors for memory corruption and system instability. The flaw directly violates the fundamental principles of memory management and can lead to arbitrary code execution when malicious actors exploit the dangling pointer references. This vulnerability aligns with CWE-416, which specifically addresses the use of freed memory conditions, and represents a classic example of improper memory management within embedded operating system components. The attack surface expands significantly when considering that FreeRTOS+FAT is widely deployed in IoT devices, industrial control systems, and embedded applications where file system integrity is paramount for system reliability and security.
The technical exploitation of this vulnerability requires understanding the memory lifecycle within the FreeRTOS+FAT implementation, where the file handler structure pxFile is deallocated but continues to be referenced in cache flushing operations. When FF_Close() executes, it releases the memory occupied by pxFile through the standard memory deallocation mechanism, yet subsequent calls to FF_FlushCache() attempt to access this freed memory location to perform disk synchronization operations. This creates a race condition where the memory management system may have already reallocated the freed memory block for other purposes, leading to unpredictable behavior when the stale pointer is dereferenced. The flaw demonstrates poor resource management practices where the system fails to properly invalidate or nullify the pointer reference after deallocation, creating a scenario where the application continues to operate on memory that is no longer guaranteed to contain valid file system data. The memory access patterns in this implementation suggest that the developers assumed the file handler would remain valid throughout the entire close operation sequence, which is fundamentally flawed in concurrent or asynchronous execution environments where memory reclamation may occur at unpredictable intervals.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling attackers to achieve privilege escalation or system compromise within embedded environments that rely on FreeRTOS+FAT for file operations. When the system attempts to flush cached data to disk after a file has been closed, the use-after-free condition can result in data corruption, system crashes, or even allow malicious actors to inject code into the system through carefully crafted file operations. The vulnerability particularly affects IoT devices, medical equipment, automotive systems, and industrial automation where FreeRTOS+FAT is commonly implemented, as these systems often operate with limited security monitoring capabilities and may not detect or recover from memory corruption errors. The attack vector becomes more sophisticated when considering that this vulnerability can be triggered through normal file system operations, making it difficult to distinguish between legitimate system behavior and malicious exploitation attempts. Organizations deploying systems using this library face significant risk of persistent system instability, data integrity issues, and potential unauthorized access to sensitive information stored on affected devices.
Mitigation strategies for CVE-2019-18178 require immediate implementation of software patches provided by Real Time Engineers, as the vulnerability cannot be effectively addressed through configuration changes alone due to its fundamental nature in the memory management implementation. The recommended approach involves updating to the latest version of FreeRTOS+FAT where the use-after-free condition has been resolved through proper pointer invalidation and memory management practices. Security teams should conduct comprehensive vulnerability assessments across all systems utilizing affected FreeRTOS+FAT versions, particularly focusing on embedded devices that may be exposed to network access or have critical operational functions. Organizations should implement additional runtime monitoring to detect anomalous memory access patterns and file system behavior that could indicate exploitation attempts. The remediation process must include thorough regression testing to ensure that the patch does not introduce new functionality issues or performance degradation in existing systems. Additionally, system architects should consider implementing memory safety mechanisms such as stack canaries, address space layout randomization, and memory access controls to provide defense-in-depth protection against similar vulnerabilities. The ATT&CK framework categorizes this vulnerability under T1059 for execution through system commands and T1490 for data destruction, highlighting the potential for both operational disruption and data compromise. Organizations should also review their supply chain security processes to ensure that embedded components are regularly updated and that security patches are applied in a timely manner to prevent exploitation of known vulnerabilities in deployed systems.