CVE-2001-0861 in IOS
Summary
by MITRE
Cisco 12000 with IOS 12.0 and line cards based on Engine 2 and earlier allows remote attackers to cause a denial of service (CPU consumption) by flooding the router with traffic that generates a large number of ICMP Unreachable replies.
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Analysis
by VulDB Data Team • 05/06/2019
The vulnerability identified as CVE-2001-0861 represents a significant denial of service weakness in Cisco 12000 series routers operating with IOS version 12.0 and line cards utilizing Engine 2 or earlier hardware architectures. This flaw specifically targets the router's handling of Internet Control Message Protocol traffic, creating a condition where malicious actors can exploit the system's response mechanisms to consume excessive CPU resources. The vulnerability manifests when the router receives a flood of traffic patterns that trigger the generation of numerous ICMP Unreachable messages, effectively overwhelming the device's processing capabilities. This issue falls under the category of resource exhaustion attacks that target fundamental network infrastructure components, making it particularly dangerous in operational technology environments where continuous network availability is critical.
The technical implementation of this vulnerability stems from insufficient input validation and inadequate traffic handling mechanisms within the router's IOS processing engine. When the affected Cisco 12000 routers encounter specific traffic patterns that result in multiple ICMP Unreachable messages being generated, the system's CPU utilization spikes dramatically as it attempts to process and respond to each individual message. This behavior creates a feedback loop where the router's response to the attack traffic generates additional traffic, amplifying the resource consumption problem. The flaw is particularly insidious because it operates at the network layer, affecting the fundamental routing capabilities of the device rather than just application-level services. According to CWE classification, this vulnerability maps to CWE-400: Uncontrolled Resource Consumption, which encompasses various forms of resource exhaustion attacks that can lead to system instability and denial of service conditions.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire network infrastructures, especially in environments where Cisco 12000 routers serve as critical core components. Attackers can leverage this weakness to create sustained denial of service conditions that may persist until manual intervention occurs or the device is restarted. The attack vector requires only the ability to send specific traffic patterns to the targeted router, making it accessible to adversaries with minimal technical expertise. Network administrators face significant challenges in detecting and mitigating this attack because the symptoms appear as normal CPU utilization spikes rather than obvious malicious activity patterns. This vulnerability demonstrates the importance of proper traffic handling and resource management in network infrastructure devices, as it exposes how seemingly benign network protocols can be weaponized to create substantial operational disruptions. The impact is particularly severe in mission-critical environments where network availability is paramount, as this vulnerability can effectively render the router unusable and potentially compromise downstream network services.
Mitigation strategies for CVE-2001-0861 require a multi-layered approach combining immediate defensive measures with long-term architectural improvements. Network administrators should implement rate limiting mechanisms to control the volume of ICMP traffic passing through affected routers, while also configuring access control lists to filter out suspicious traffic patterns that could trigger the vulnerability. The most effective immediate solution involves upgrading to newer IOS versions that contain patches addressing this specific issue, as Cisco released updates to resolve the underlying processing flaws in their software implementations. Additionally, implementing network segmentation and traffic monitoring systems can help detect anomalous traffic patterns that might indicate exploitation attempts. Organizations should also consider deploying intrusion detection systems that can identify the specific traffic signatures associated with this attack vector. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving resource exhaustion and network denial of service, emphasizing the need for defensive measures that protect against both active exploitation and passive monitoring of network infrastructure components. The vulnerability underscores the critical importance of maintaining up-to-date network device firmware and implementing comprehensive network security monitoring to prevent exploitation of known weaknesses in core infrastructure components.