CVE-2015-6496 in NetFilter
Summary
by MITRE
conntrackd in conntrack-tools 1.4.2 and earlier does not ensure that the optional kernel modules are loaded before using them, which allows remote attackers to cause a denial of service (crash) via a (1) DCCP, (2) SCTP, or (3) ICMPv6 packet.
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Analysis
by VulDB Data Team • 11/18/2024
The vulnerability identified as CVE-2015-6496 affects conntrackd within the conntrack-tools suite version 1.4.2 and earlier, presenting a critical denial of service risk that stems from improper handling of kernel module dependencies. This flaw specifically targets the connection tracking daemon's inability to verify that essential kernel modules are loaded before attempting to utilize their functionality, creating a scenario where remote attackers can exploit this oversight to crash the system through carefully crafted network packets.
The technical implementation of this vulnerability resides in the conntrackd daemon's failure to perform proper module availability checks before invoking kernel-level functions. When processing incoming network traffic, the daemon attempts to handle DCCP SCTP and ICMPv6 protocols without first confirming that the corresponding kernel modules are properly loaded and available. This oversight creates a race condition where the system attempts to access kernel functionality that may not yet be initialized or available, resulting in kernel panics and system crashes.
The operational impact of CVE-2015-6496 extends beyond simple service disruption, as it represents a fundamental design flaw in the connection tracking infrastructure that affects network security appliances, firewalls, and systems relying on connection tracking for traffic management. Attackers can exploit this vulnerability by simply sending malformed packets of the specified protocols to a vulnerable system, making the attack surface extremely broad and the exploitation relatively simple. The vulnerability aligns with CWE-470, which addresses the use of insecure functions, and specifically relates to the improper handling of external dependencies in kernel module management.
Systems utilizing conntrackd for connection tracking are particularly vulnerable when deployed in environments where DCCP SCTP or ICMPv6 traffic is processed, including enterprise firewalls, network security appliances, and Linux-based systems implementing connection tracking for traffic control. The vulnerability affects any system running conntrack-tools version 1.4.2 or earlier, regardless of the underlying network infrastructure, making it a widespread concern across various network security implementations. Organizations implementing network monitoring and traffic filtering solutions that rely on connection tracking functionality are at significant risk of experiencing service interruptions and potential system crashes.
The mitigation strategy for CVE-2015-6496 requires immediate upgrading to conntrack-tools version 1.4.3 or later, which includes proper kernel module dependency checking and loading mechanisms. Additionally, network administrators should implement proactive monitoring of connection tracking processes and ensure that all required kernel modules are properly initialized and available before system deployment. Organizations should also consider implementing network segmentation and access controls to limit exposure to this vulnerability, while maintaining regular patch management procedures to address similar issues in other network security tools. This vulnerability demonstrates the critical importance of proper dependency management in kernel-level applications and aligns with ATT&CK technique T1499, which addresses network denial of service attacks through system resource exhaustion or kernel-level disruptions.