CVE-2018-1114 in Undertow
Summary
by MITRE
It was found that URLResource.getLastModified() in Undertow closes the file descriptors only when they are finalized which can cause file descriptors to exhaust. This leads to a file handler leak.
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Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2018-1114 resides within the Undertow web server implementation and represents a critical resource management flaw that can lead to system instability and denial of service conditions. This issue specifically affects the URLResource.getLastModified() method which is responsible for retrieving modification timestamps from files within the web server's resource handling framework. The flaw manifests when the method fails to properly close file descriptors immediately after use, instead relying on garbage collection finalization processes to release these system resources. This design oversight creates a scenario where file handles remain open indefinitely until the Java garbage collector executes its finalization routines, which can occur at unpredictable intervals or may not occur at all under certain memory pressure conditions. The vulnerability directly impacts the operating system's file descriptor limits, which are typically constrained to prevent system resource exhaustion and maintain stability across all running processes. When multiple requests are processed through the affected Undertow implementation, each request that invokes URLResource.getLastModified() accumulates open file descriptors that are not released promptly, leading to progressive resource consumption that eventually exhausts the available file descriptor pool.
The technical nature of this vulnerability aligns with CWE-404, which describes improper resource cleanup or release, and specifically relates to the improper handling of file descriptors within the Java Virtual Machine's resource management framework. The flaw demonstrates characteristics consistent with the ATT&CK technique T1499.004, which involves resource exhaustion attacks through file descriptor manipulation, where an attacker can exploit the delayed cleanup behavior to consume system resources and potentially cause service disruption. The operational impact of this vulnerability extends beyond simple resource leakage, as it creates a persistent condition that can degrade system performance over time and ultimately lead to complete service unavailability when the file descriptor limit is reached. Applications running on affected Undertow versions may experience increasing latency, failed request processing, and system crashes when the underlying operating system prevents new file descriptor allocations due to exhaustion.
Mitigation strategies for CVE-2018-1114 require immediate attention through patching the Undertow library to version 2.0.15 or later, which contains the necessary fixes to ensure proper file descriptor cleanup during URLResource.getLastModified() operations. Organizations should implement monitoring solutions to track file descriptor usage across their Undertow-based applications and establish alerting thresholds that trigger before reaching critical exhaustion levels. System administrators should also consider implementing process-level file descriptor limits and resource management policies that can help contain the impact of such leaks even when the underlying vulnerability persists. Additionally, application developers should review their code for any direct or indirect usage of URLResource.getLastModified() and implement proper resource management patterns that explicitly close file handles when possible. The fix addresses the root cause by ensuring that file descriptors are closed immediately upon method completion rather than relying on garbage collection finalization, thereby preventing the accumulation of open file handles that can lead to system resource exhaustion and denial of service conditions.