CVE-2018-0155 in Catalyst 4500
Summary
by MITRE
A vulnerability in the Bidirectional Forwarding Detection (BFD) offload implementation of Cisco Catalyst 4500 Series Switches and Cisco Catalyst 4500-X Series Switches could allow an unauthenticated, remote attacker to cause a crash of the iosd process, causing a denial of service (DoS) condition. The vulnerability is due to insufficient error handling when the BFD header in a BFD packet is incomplete. An attacker could exploit this vulnerability by sending a crafted BFD message to or across an affected switch. A successful exploit could allow the attacker to trigger a reload of the system. This vulnerability affects Catalyst 4500 Supervisor Engine 6-E (K5), Catalyst 4500 Supervisor Engine 6L-E (K10), Catalyst 4500 Supervisor Engine 7-E (K10), Catalyst 4500 Supervisor Engine 7L-E (K10), Catalyst 4500E Supervisor Engine 8-E (K10), Catalyst 4500E Supervisor Engine 8L-E (K10), Catalyst 4500E Supervisor Engine 9-E (K10), Catalyst 4500-X Series Switches (K10), Catalyst 4900M Switch (K5), Catalyst 4948E Ethernet Switch (K5). Cisco Bug IDs: CSCvc40729.
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability described in CVE-2018-0155 represents a critical denial of service weakness within the Bidirectional Forwarding Detection protocol implementation of Cisco's enterprise networking infrastructure. This flaw specifically affects the BFD offload functionality present in various Catalyst 4500 Series and 4500-X Series switches, creating a pathway for remote attackers to disrupt network operations without requiring authentication credentials. The vulnerability stems from inadequate error handling mechanisms within the switch's iosd process, which is responsible for managing the BFD protocol implementation and maintaining network connectivity monitoring functions.
The technical exploitation of this vulnerability occurs through the transmission of malformed BFD packets that contain incomplete headers, a condition that the affected switches fail to properly validate or reject. When these crafted packets are processed by the switch's BFD offload engine, the insufficient error handling causes the iosd process to crash and subsequently restart, potentially leading to a complete system reload. This behavior aligns with CWE-248, which describes improper exception handling in software systems, and represents a classic example of how protocol implementation flaws can create denial of service conditions. The vulnerability affects multiple supervisor engine variants including the 6-E, 6L-E, 7-E, 7L-E, 8-E, 8L-E, and 9-E models, as well as the 4500-X series and related Catalyst switches.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively paralyze network infrastructure by forcing system reloads at critical moments. Network administrators may experience extended downtime while systems recover from the crashes, potentially affecting mission-critical applications and services that depend on stable network connectivity. The remote nature of the attack means that adversaries can exploit this weakness from outside the network perimeter, making it particularly dangerous for organizations that do not properly segment their network infrastructure. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique involving network disruption through service availability attacks, and represents a significant threat to network resilience and availability.
Cisco has addressed this vulnerability through software updates that improve error handling within the BFD packet processing logic, requiring affected organizations to apply the appropriate security patches to their network infrastructure. The fix specifically targets the incomplete header validation process and implements more robust error handling mechanisms to prevent the iosd process from crashing when malformed BFD packets are received. Organizations should prioritize patching efforts for all affected supervisor engine models and consider implementing network segmentation or access control measures to limit exposure while updates are deployed. The vulnerability serves as a reminder of the importance of proper protocol implementation and error handling in network infrastructure devices, where even seemingly minor implementation flaws can result in significant operational disruptions and potential security risks.