CVE Alert: CVE-2025-20340 – Cisco – Cisco IOS XR Software
CVE-2025-20340
A vulnerability in the Address Resolution Protocol (ARP) implementation of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to trigger a broadcast storm, leading to a denial of service (DoS) condition on an affected device. This vulnerability is due to how Cisco IOS XR Software processes a high, sustained rate of ARP traffic hitting the management interface. Under certain conditions, an attacker could exploit this vulnerability by sending an excessive amount of traffic to the management interface of an affected device, overwhelming its ARP processing capabilities. A successful exploit could result in degraded device performance, loss of management connectivity, and complete unresponsiveness of the system, leading to a DoS condition.
AI Summary Analysis
Risk verdict
High risk of denial-of-service via ARP traffic flooding the management interface from an adjacent network; no public exploitation observed, but exposure and impact depend on reachability of the management plane.
Why this matters
An attacker on the same broadcast domain can overwhelm ARP processing, potentially isolating or degrading device management connectivity and affecting control-plane availability. In environments where management access is reachable from nearby networks, a sustained ARP flood could disrupt monitoring, remediation, and service continuity.
Most likely attack path
An attacker uses low-effort, adjacent-network access to send a high rate of ARP traffic targeting the device’s management interface. With no privileges or user interaction required, sustained traffic can exhaust ARP resources (UI and control-plane impact), causing DoS and degraded performance across dependent services.
Who is most exposed
Locations where management interfaces are exposed to adjacent networks, such as data-centre cores, service-provider edge gear, or loosely segmented enterprise networks, are most at risk. Environments with flat or poorly segmented management networks are especially vulnerable.
Detection ideas
- Spike in ARP traffic directed at management interfaces; correlate with rising CPU/memory on affected devices.
- Unusual ARP table churn or repeated ARP failures from multiple sources.
- Management-interface interfaces showing saturation, high drops, or errors during bursts.
- Anomalous NetFlow/telemetry indicating ARP storm-like patterns.
- Logs showing rapid ARP requests/responses outside normal patterns.
Mitigation and prioritisation
- Apply vendor-recommended patches or upgrade to fixed releases; prioritise if the management plane is reachable from adjacent networks.
- Restrict ARP traffic to trusted sources via ACLs on edge and aggregation devices; segment management networks (VLANs, firewalls, or dedicated links).
- Enable ARP rate-limiting and ARP inspection/validation on management interfaces.
- Disable or tightly restrict unused management paths; implement strong network segmentation and access controls.
- Plan tested, staged deployments with monitoring windows; establish baseline ARP activity for rapid alerting.
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