CVE-2015-6359 in IOS XE
Summary
by MITRE
The Neighbor Discovery (ND) protocol implementation in the IPv6 stack in Cisco IOS 15.3(3)S0.1 on ASR devices mishandles internal tables, which allows remote attackers to cause a denial of service (memory consumption or device crash) via a flood of crafted ND messages, aka Bug ID CSCup28217.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability identified as CVE-2015-6359 represents a critical flaw in the IPv6 Neighbor Discovery protocol implementation within Cisco IOS software running on ASR (Autonomous System Router) devices. This issue specifically affects Cisco IOS version 15.3(3)S0.1 and demonstrates a fundamental weakness in how the system processes Neighbor Discovery messages, creating a pathway for remote attackers to exploit the device's memory management and operational stability. The flaw resides in the internal table handling mechanisms that govern how IPv6 neighbor information is stored and maintained within the routing infrastructure.
The technical execution of this vulnerability involves crafting specially formatted Neighbor Discovery messages that trigger improper memory allocation and table management within the affected IOS implementation. When these malicious packets are flooded toward the target device, they cause the system to consume excessive memory resources or trigger a complete system crash through improper state handling. The underlying mechanism involves the failure to properly validate or limit the growth of internal neighbor tables, allowing attackers to exhaust system resources through sustained message flooding. This type of attack falls under the category of resource exhaustion attacks and specifically targets the IPv6 stack's memory management capabilities, making it particularly dangerous for network infrastructure devices that must maintain neighbor information for proper routing operations.
The operational impact of CVE-2015-6359 extends beyond simple service disruption to potentially compromising entire network segments that depend on the affected ASR devices for routing functionality. When a device experiences a denial of service condition due to this vulnerability, it can result in complete network partitioning as routing information becomes unavailable and traffic cannot be properly forwarded. Network administrators may find their devices becoming unresponsive or requiring manual reboot to restore normal operation, creating significant downtime and operational disruption. The vulnerability is particularly concerning because it affects core routing infrastructure components that are often deployed in mission-critical network environments where availability is paramount.
Mitigation strategies for this vulnerability should include immediate implementation of access control lists to filter malicious Neighbor Discovery traffic, enabling rate limiting on IPv6 neighbor discovery messages, and applying the relevant Cisco IOS software patches that address the internal table handling flaws. Network segmentation and monitoring solutions should be deployed to detect unusual flooding patterns of Neighbor Discovery messages that may indicate exploitation attempts. The vulnerability aligns with CWE-129, which addresses improper validation of array index values, and represents a classic example of how insufficient input validation can lead to resource exhaustion attacks. From an ATT&CK framework perspective, this vulnerability maps to techniques involving resource exhaustion and denial of service, specifically targeting network infrastructure components through protocol manipulation. Organizations should also consider implementing network monitoring to detect anomalous Neighbor Discovery traffic patterns and establish incident response procedures for handling such exploitation attempts.