CVE-2014-3293 in ASR901
Summary
by MITRE
Cisco IOS 15.4(3)S0b on ASR901 devices makes incorrect decisions to use the CPU for IPv4 packet processing, which allows remote attackers to cause a denial of service (BGP neighbor flapping) by sending many crafted IPv4 packets, aka Bug ID CSCuo29736.
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Analysis
by VulDB Data Team • 06/10/2017
Cisco IOS version 15.4(3)S0b running on ASR901 devices contains a critical vulnerability that manifests through improper CPU utilization during IPv4 packet processing. This flaw specifically affects the Border Gateway Protocol implementation where the system incorrectly routes packet processing tasks to the CPU instead of leveraging hardware acceleration. The vulnerability stems from inadequate packet validation mechanisms within the routing engine that fail to properly distinguish between legitimate traffic and crafted malicious packets designed to trigger the faulty processing path. Attackers can exploit this weakness by transmitting specifically formatted IPv4 packets that cause the device to repeatedly switch between active and inactive BGP neighbor states, creating a condition known as neighbor flapping that ultimately results in complete service disruption.
The technical implementation of this vulnerability resides in the packet processing pipeline where the IOS kernel fails to properly validate packet headers and routing information before determining processing priority. When crafted packets arrive, the system's decision-making algorithm incorrectly evaluates the packet characteristics and assigns CPU-intensive processing tasks to what should be hardware-accelerated operations. This misclassification triggers a cascade of events where the BGP daemon repeatedly attempts to establish and tear down neighbor connections, consuming significant system resources and causing the device to become unresponsive. The vulnerability operates at the network layer and affects the control plane functionality, making it particularly dangerous as it impacts routing decisions and network stability. According to CWE classification, this represents a weakness in resource management and input validation, specifically categorized under CWE-20 Improper Input Validation and CWE-400 Uncontrolled Resource Consumption.
The operational impact of this vulnerability extends beyond simple denial of service, as it can cause widespread network instability and service degradation across connected infrastructure. BGP neighbor flapping disrupts routing convergence and can lead to packet loss, increased latency, and potential network partitioning effects that cascade through the entire routing domain. Network administrators may observe frequent routing table updates, increased CPU utilization, and intermittent connectivity issues that are difficult to diagnose due to the indirect nature of the attack vector. The vulnerability affects devices in production environments where BGP is actively used for external routing, making it particularly dangerous for service providers and enterprise networks that rely on stable routing protocols. This weakness can be exploited by attackers with minimal privileges to cause significant operational disruption, as demonstrated by the specific bug ID CSCuo29736 that was documented by Cisco.
Mitigation strategies for this vulnerability require immediate implementation of software updates and patches provided by Cisco to address the faulty packet processing logic. Network administrators should prioritize applying the relevant IOS software updates that correct the decision-making algorithms in the BGP implementation and restore proper hardware acceleration usage. Additionally, implementing traffic filtering mechanisms at network boundaries can help reduce the impact by limiting the volume of crafted packets that reach affected devices. The use of BGP monitoring tools and anomaly detection systems can aid in early identification of neighbor flapping behavior, allowing for faster response times. Network segmentation and access control policies should be reviewed to limit exposure of vulnerable devices to untrusted networks, while implementing rate limiting on BGP sessions can help prevent rapid neighbor state changes. Organizations should also consider implementing redundant routing paths and failover mechanisms to minimize the impact of potential exploitation attempts, as outlined in the ATT&CK framework's methodology for network service disruption techniques.