CVE-2018-0369 in StarOS
Summary
by MITRE
A vulnerability in the reassembly logic for fragmented IPv4 packets of Cisco StarOS running on virtual platforms could allow an unauthenticated, remote attacker to trigger a reload of the npusim process, resulting in a denial of service (DoS) condition. There are four instances of the npusim process running per Service Function (SF) instance, each handling a subset of all traffic flowing across the device. It is possible to trigger a reload of all four instances of the npusim process around the same time. The vulnerability is due to improper handling of fragmented IPv4 packets containing options. An attacker could exploit this vulnerability by sending a malicious IPv4 packet across an affected device. An exploit could allow the attacker to trigger a restart of the npusim process, which will result in all traffic queued toward this instance of the npusim process to be dropped while the process is restarting. The npusim process typically restarts within less than a second. This vulnerability affects: Cisco Virtualized Packet Core-Single Instance (VPC-SI), Cisco Virtualized Packet Core-Distributed Instance (VPC-DI), Cisco Ultra Packet Core (UPC). Cisco Bug IDs: CSCvh29613.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 04/09/2023
The vulnerability described in CVE-2018-0369 represents a critical denial of service weakness within Cisco StarOS software operating on virtual platforms, specifically impacting the packet reassembly functionality for fragmented ipv4 traffic. This flaw exists in the network processing logic that handles fragmented packets containing ip options, creating a pathway for remote exploitation without authentication requirements. The affected systems include Cisco Virtualized Packet Core Single Instance and Distributed Instance configurations as well as Cisco Ultra Packet Core deployments, indicating a broad impact across multiple virtualized network infrastructure solutions. The vulnerability stems from inadequate validation and processing of fragmented ipv4 packets that contain ip options, which are used to modify packet behavior and provide additional packet processing capabilities.
The technical implementation of this vulnerability manifests through improper handling of fragmented ipv4 packets that contain ip options within the npusim process execution environment. The npusim process serves as a critical component within Cisco StarOS architecture, with four instances operating per Service Function instance to manage traffic distribution across the device. When an attacker crafts and transmits maliciously formatted ipv4 packets containing fragmented data with ip options, the reassembly logic fails to properly validate or process these packets, leading to unexpected behavior in the npusim process. This improper handling causes the process to enter a state where it must be restarted, triggering a cascading effect that affects all four npusim instances simultaneously within the same Service Function instance. The process restart occurs rapidly, typically within less than a second, but during this brief window all traffic queued for processing by that specific npusim instance is dropped, creating temporary service disruption.
The operational impact of this vulnerability extends beyond simple service interruption, as it represents a potential vector for sustained denial of service attacks that could degrade network performance and availability. The npusim process restarts are not merely temporary inconveniences but actual system reload events that temporarily drop all queued traffic, potentially affecting network connectivity and service delivery for the duration of the process restart cycle. Since this vulnerability affects multiple service function instances simultaneously, an attacker could potentially cause widespread disruption across affected network infrastructure. The vulnerability is particularly concerning because it operates at the packet processing layer, meaning that legitimate traffic can be disrupted by malicious packet injection, and the attack requires no authentication credentials, making it accessible to any remote attacker with network access. This characteristic places the vulnerability in the context of network-level attacks that can be executed at scale without requiring specialized privileges or insider knowledge of the target system.
Organizations affected by this vulnerability should implement immediate mitigation strategies focusing on network segmentation and traffic monitoring to detect potential exploitation attempts. The recommended approach includes deploying intrusion detection systems that can identify malformed fragmented ipv4 packets containing ip options, implementing rate limiting on fragmented packet processing, and establishing monitoring protocols to detect npusim process restarts. Network administrators should also consider implementing access control lists that filter out suspicious fragmented traffic patterns and ensure that all affected devices receive the appropriate software patches provided by Cisco. The vulnerability aligns with attack patterns documented in the mitre attack framework under network infiltration and denial of service tactics, specifically targeting the network infrastructure layer. From a cwe perspective, this vulnerability maps to cwe-129, which addresses improper validation of input boundaries, and cwe-20, which covers input validation weaknesses, though the specific manifestation occurs in the packet reassembly logic rather than traditional input validation contexts. Organizations should also consider implementing redundancy mechanisms and failover procedures to minimize the impact of potential service disruptions while patches are being deployed across their infrastructure.