CVE-2015-6431 in IOS XE
Summary
by MITRE
Cisco IOS XE 16.1.1 allows remote attackers to cause a denial of service (device reload) via a packet with the 00-00-00-00-00-00 source MAC address, aka Bug ID CSCux48405.
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Analysis
by VulDB Data Team • 06/19/2018
Cisco IOS XE software version 16.1.1 contains a critical vulnerability that enables remote attackers to induce a device reload through the careful crafting of network packets with a specific source MAC address. This vulnerability manifests when the system receives packets containing the hexadecimal sequence 00-00-00-00-00-00 as the source media access control address, which represents a null MAC address that should never appear in legitimate network traffic. The flaw exists within the packet processing logic of the network operating system, where the device fails to properly validate or handle these malformed packets, leading to an unexpected system state that triggers an automatic device restart.
The technical implementation of this vulnerability stems from insufficient input validation mechanisms within the IOS XE packet handling subsystem. When a packet with the null MAC address is processed, the system's network stack encounters a condition that causes an unhandled exception or memory corruption within the kernel-level packet processing routines. This specific MAC address pattern bypasses normal validation checks that would typically filter out malformed or invalid network traffic, allowing the packet to traverse the normal packet processing pipeline until it reaches a point where the system cannot properly handle the null address value. The vulnerability operates at the data link layer of the OSI model, specifically affecting the Ethernet frame processing capabilities of the network device.
The operational impact of this vulnerability extends beyond simple denial of service, as it provides attackers with a method to repeatedly disrupt network services without requiring authentication or privileged access. Remote attackers can exploit this weakness from any location on the network, making it particularly dangerous in environments where network devices are exposed to untrusted traffic. The device reload caused by this vulnerability creates a cascading effect that can disrupt network connectivity, potentially affecting multiple network segments depending on the role of the compromised device. Network administrators may experience service interruptions that could last several minutes while the device reboots and re-establishes network connections, leading to potential business disruption and increased operational overhead.
Mitigation strategies for this vulnerability should focus on implementing network access control lists to filter out packets with null MAC addresses at the network perimeter, as well as applying the official Cisco security patches released for IOS XE 16.1.1. Organizations should also consider implementing network segmentation to limit the potential impact of such attacks and establish monitoring procedures to detect unusual device restart patterns that may indicate exploitation attempts. The vulnerability aligns with CWE-129, Input Validation, and represents a specific instance of improper validation of input data, while also mapping to ATT&CK technique T1499.002 for network denial of service attacks. Network security teams should prioritize patch management for affected systems and implement continuous monitoring to detect potential exploitation attempts that could leverage this weakness to cause sustained network disruption.