CVE-2018-5739 in Kea
Summary
by MITRE
An extension to hooks capabilities which debuted in Kea 1.4.0 introduced a memory leak for operators who are using certain hooks library facilities. In order to support multiple requests simultaneously, Kea 1.4 added a callout handle store but unfortunately the initial implementation of this store does not properly free memory in every case. Hooks which make use of query4 or query6 parameters in their callouts can leak memory, resulting in the eventual exhaustion of available memory and subsequent failure of the server process. Affects Kea DHCP 1.4.0.
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Analysis
by VulDB Data Team • 07/01/2023
The vulnerability described in CVE-2018-5739 represents a critical memory management flaw within the Kea DHCP server version 1.4.0 that emerged from an enhanced hooks capability introduced in this release. This issue specifically impacts the memory cleanup mechanisms within the callout handle store implementation that was added to support concurrent request processing. The flaw manifests when operators utilize certain hooks library facilities, particularly those that employ query4 or query6 parameters in their callout operations. The root cause lies in the incomplete memory deallocation logic within the initial implementation of the callout handle store, which fails to properly release allocated memory resources under all execution paths. This memory leak occurs incrementally with each use of affected hooks, creating a gradual accumulation of unreleased memory segments that eventually consumes all available system memory resources.
The technical impact of this vulnerability extends beyond simple resource consumption to represent a potential denial of service condition that can completely compromise the DHCP server functionality. When the memory leak reaches critical levels, the server process fails due to memory exhaustion, rendering the DHCP service unavailable to clients seeking network configuration. The vulnerability affects the core operational stability of Kea DHCP servers deployed in production environments where hooks are actively utilized for custom processing of DHCP requests. The flaw specifically targets the memory management subsystem rather than network protocols or authentication mechanisms, making it particularly insidious as it operates at the application level without generating obvious network-level indicators of compromise. According to CWE classification, this vulnerability maps to CWE-401: Improper Release of Memory Before Removing Last Reference, which describes the failure to properly deallocate memory resources when they are no longer needed.
From an operational perspective, this vulnerability creates a significant risk for network infrastructure administrators who rely on Kea DHCP servers for critical network operations. The memory leak occurs gradually over time, making it difficult to detect during routine monitoring but ultimately leading to complete service failure. The impact is particularly severe in high-traffic environments where DHCP requests are frequent and hooks are extensively used for custom processing. Network administrators may observe increasing memory usage patterns in system monitoring tools before the final service failure occurs, but the gradual nature of the leak makes proactive detection challenging. The vulnerability affects the fundamental availability of the DHCP service, which can disrupt network connectivity for all clients relying on dynamic IP address assignment.
The recommended mitigation strategies for CVE-2018-5739 focus primarily on immediate software updates to versions that contain corrected memory management implementations. Organizations should prioritize upgrading their Kea DHCP installations to versions that address this specific memory leak issue in the hooks library facilities. Additionally, system administrators should implement monitoring solutions that track memory consumption patterns for DHCP servers to detect early signs of memory exhaustion. Temporary workarounds may include reducing the use of hooks that employ query4 or query6 parameters, though this approach limits the functionality of the DHCP server. The vulnerability demonstrates the importance of thorough testing for memory management in concurrent processing systems and highlights the need for comprehensive memory leak detection during software development cycles. Security teams should also consider implementing automated restart procedures for DHCP services to minimize downtime when memory exhaustion occurs, though this represents a reactive measure rather than a permanent fix. The ATT&CK framework categorizes this vulnerability under T1499.004: Endpoint Denial of Service, as it specifically targets the availability of endpoint services through memory exhaustion techniques.