CVE-2018-0295 in NX-OS
Summary
by MITRE
A vulnerability in the Border Gateway Protocol (BGP) implementation of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition due to the device unexpectedly reloading. The vulnerability is due to incomplete input validation of the BGP update messages. An attacker could exploit this vulnerability by sending a crafted BGP update message to the targeted device. An exploit could allow the attacker to cause the switch to reload unexpectedly. The Cisco implementation of the BGP protocol only accepts incoming BGP traffic from explicitly defined peers. To exploit this vulnerability, an attacker must be able to send the malicious packets over a TCP connection that appears to come from a trusted BGP peer or inject malformed messages into the victim's BGP network. This would require obtaining information about the BGP peers in the affected system's trusted network. The vulnerability may be triggered when the router receives a malformed BGP message from a peer on an existing BGP session. At least one BGP neighbor session must be established for a router to be vulnerable. This vulnerability affects Nexus 2000 Series Switches, Nexus 3000 Series Switches, Nexus 3500 Platform Switches, Nexus 3600 Platform Switches, Nexus 5500 Platform Switches, Nexus 5600 Platform Switches, Nexus 6000 Series Switches, Nexus 7000 Series Switches, Nexus 7700 Series Switches, Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode, Nexus 9000 Series Switches in standalone NX-OS mode, Nexus 9500 R-Series Line Cards and Fabric Modules. Cisco Bug IDs: CSCve79599, CSCve87784, CSCve91371, CSCve91387.
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Analysis
by VulDB Data Team • 03/28/2023
The vulnerability described in CVE-2018-0295 represents a critical denial of service weakness within Cisco NX-OS Software implementations of the Border Gateway Protocol. This flaw manifests as an incomplete input validation mechanism in the BGP update message processing component, creating a pathway for remote attackers to induce unexpected system reloads without requiring authentication credentials. The vulnerability operates through a fundamental protocol implementation gap where the software fails to properly validate incoming BGP update messages before processing them, allowing maliciously crafted packets to trigger system instability.
The technical exploitation of this vulnerability requires an attacker to establish a TCP connection that appears to originate from a legitimate BGP peer within the trusted network, or to inject malformed BGP messages directly into the victim's BGP network infrastructure. This prerequisite aligns with ATT&CK technique T1071.004 for application layer protocol manipulation and demonstrates the need for network-level access or the ability to perform man-in-the-middle attacks against BGP sessions. The attack vector specifically targets the BGP update message processing functionality, where the system's insufficient input validation allows malformed data to propagate through the network control plane, ultimately causing the device to crash and reload.
The operational impact of this vulnerability extends across multiple Cisco Nexus product lines including 2000, 3000, 3500, 3600, 5500, 5600, 6000, 7000, 7700, and 9000 series switches, as well as specialized ACI mode configurations and standalone NX-OS deployments. This widespread scope creates significant risk for enterprise network infrastructure, particularly in environments where BGP is critical for external connectivity and inter-domain routing. The vulnerability's requirement for an established BGP neighbor session means that the attack cannot be launched against isolated devices, but rather requires access to the BGP network topology and information about trusted peer relationships.
The root cause of this vulnerability maps directly to CWE-20, which describes "Improper Input Validation" in software systems. This weakness allows attackers to inject malformed data that bypasses normal input sanitization processes, leading to unexpected behavior in the target system. The vulnerability's classification as a remote, unauthenticated DoS condition reflects the severity of the impact, as it can be exploited from outside the network perimeter without requiring any privileged access. The fact that the exploit requires only a single malformed BGP update message to cause a complete system reload demonstrates the high-impact nature of the flaw, potentially disrupting network services and causing cascading failures across dependent systems.
Mitigation strategies for this vulnerability should focus on network segmentation and BGP security hardening measures. Network administrators should implement BGP session authentication mechanisms such as MD5 authentication to prevent unauthorized peers from establishing sessions, and deploy BGP monitoring tools to detect anomalous update message patterns. The Cisco security advisories recommend implementing access control lists to filter BGP traffic and establishing proper BGP peer relationship management to minimize the attack surface. Additionally, network operators should consider implementing BGP route filtering and prefix validation to reduce the impact of malformed messages, while maintaining regular software update schedules to ensure deployment of the vendor's security patches. This vulnerability highlights the importance of robust input validation in network protocol implementations and the need for continuous security assessment of core routing protocols that form the backbone of internet connectivity.