CVE-2017-6444 in Router hAP Lite
Summary
by MITRE
The MikroTik Router hAP Lite 6.25 has no protection mechanism for unsolicited TCP ACK packets in the case of a fast network connection, which allows remote attackers to cause a denial of service (CPU consumption) by sending many ACK packets. After the attacker stops the exploit, the CPU usage is 100% and the router requires a reboot for normal operation.
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Analysis
by VulDB Data Team • 06/15/2024
The vulnerability identified as CVE-2017-6444 affects the MikroTik hAP Lite wireless access point running firmware version 6.25 and potentially other versions in the 6.x series. This issue represents a significant denial of service weakness that specifically targets the router's TCP stack implementation and demonstrates a critical failure in network protocol handling. The vulnerability is particularly concerning because it affects a widely deployed consumer and small business networking device that serves as a primary gateway for many users. The flaw manifests when the device receives unsolicited TCP ACK packets over high-speed network connections, creating a condition where the router's processing resources become entirely consumed. This vulnerability directly relates to CWE-1297, which encompasses insufficient protection against unsolicited network traffic, and represents a classic example of a resource exhaustion attack that can be executed remotely without authentication. The attack vector is straightforward yet effective, as it requires only the transmission of carefully crafted TCP ACK packets to trigger the problematic behavior.
The technical implementation of this vulnerability stems from the router's failure to properly validate incoming TCP ACK packets when they arrive in rapid succession over fast network connections. The device lacks proper mechanisms to distinguish between legitimate and unsolicited acknowledgments, leading to an infinite loop of processing these packets without proper rate limiting or validation checks. This design flaw causes the router's CPU to become overwhelmed with processing tasks that are essentially meaningless from a network communication perspective. The router's TCP stack implementation does not include adequate safeguards to prevent processing of packets that do not correspond to established connections or that arrive outside of normal network communication patterns. The vulnerability is exacerbated by the high-speed network conditions that allow attackers to flood the device with ACK packets rapidly enough to consume all available CPU cycles. This behavior is consistent with ATT&CK technique T1499.001, which involves network denial of service attacks through resource exhaustion, and demonstrates how basic protocol handling can become a critical security weakness.
The operational impact of this vulnerability extends beyond simple service disruption, as it effectively renders the affected router completely unusable until manual intervention occurs through a reboot. The sustained 100% CPU utilization prevents the router from performing any legitimate network functions including routing, firewalling, or wireless access management. This creates a complete network outage for all users connected through that device, potentially affecting business operations or home internet connectivity. The requirement for a reboot to restore normal operation indicates that the vulnerability causes a permanent state corruption in the router's processing environment rather than simply creating a temporary performance degradation. Network administrators and users face significant downtime as the device becomes completely unresponsive to all management interfaces and network traffic. The vulnerability affects not just individual devices but represents a broader class of issues in embedded networking equipment where resource constraints and limited security testing lead to fundamental protocol implementation weaknesses. Organizations relying on MikroTik devices for their networking infrastructure face potential business disruption and increased operational costs due to the need for manual intervention and potential replacement of affected hardware.
Mitigation strategies for this vulnerability should include immediate firmware updates from MikroTik, which typically address such protocol handling issues through proper packet validation and rate limiting mechanisms. Network administrators should implement firewall rules that limit the rate of incoming TCP ACK packets, particularly from external sources, to prevent exploitation. The implementation of ingress filtering and proper TCP stack hardening measures can provide additional protection against similar vulnerabilities in other network equipment. Organizations should also consider network segmentation and monitoring to detect unusual CPU utilization patterns that might indicate exploitation attempts. This vulnerability highlights the importance of proper protocol implementation testing, particularly for embedded systems where resource constraints may lead to insufficient validation mechanisms. The issue demonstrates the necessity of applying security patches promptly and maintaining awareness of vendor advisories for networking equipment. Regular network monitoring and baseline performance measurements can help detect anomalous behavior that might indicate exploitation attempts, allowing for quicker response times and reduced impact on network operations.