Introduction
Loss of management access to a core router can bring critical operations to a halt. In large service provider environments, a single broadcast storm on the management network can cause widespread outages and require manual intervention at remote sites.
Cisco IOS XR is the flagship network operating system for Cisco's high-end routers, including the ASR 9000 and NCS series, widely deployed in carrier and enterprise backbones. Its reliability is central to internet infrastructure worldwide. Cisco, as a vendor, holds a dominant position in the global networking market and is responsible for a significant share of the world's critical routing infrastructure.
Technical Information
CVE-2025-20340 is a denial of service vulnerability in the Address Resolution Protocol (ARP) implementation of Cisco IOS XR Software. The vulnerability is triggered when the management interface of an affected device receives a high, sustained rate of ARP traffic.
The ARP processing logic in IOS XR does not adequately limit or police the rate of ARP requests directed at the management interface. When an attacker with network adjacency (i.e., on the same L2 segment) sends excessive ARP requests, the device's ARP subsystem becomes overwhelmed. This leads to uncontrolled resource consumption (CWE-400), resulting in a broadcast storm and denial of service.
Affected devices may experience:
- Degraded performance
- Loss of management connectivity
- Complete unresponsiveness, requiring manual recovery
The root cause is insufficient rate limiting or resource allocation for ARP traffic on management interfaces. The vulnerability is not known to be triggered by malformed packets but rather by volume and sustained traffic rates. No public code snippets or configuration examples are available that directly demonstrate the vulnerable logic.
Affected Systems and Versions
- Cisco IOS XR Software (specific versions not enumerated in public sources)
- Devices with management interfaces exposed to adjacent network segments
- Vulnerable when ARP rate limiting or storm control is not properly configured on management interfaces
No exact version numbers or ranges are listed in public sources as of the advisory publication.
Vendor Security History
Cisco has a history of resource exhaustion and management plane vulnerabilities in IOS XR:
- CVE-2025-20115: BGP DoS via confederation processing
- CVE-2025-20138: Privilege escalation in CLI
- CVE-2025-20154: TWAMP DoS in IOS, XE, and XR
Cisco's patch response times have improved, with advisories and mitigations typically published quickly. However, resource exhaustion and management plane vulnerabilities are recurring themes, indicating ongoing architectural challenges.