CVE-2025-20189 in IOS XE
Summary
by MITRE • 05/07/2025
A vulnerability in the Cisco Express Forwarding functionality of Cisco IOS XE Software for Cisco ASR 903 Aggregation Services Routers with Route Switch Processor 3 (RSP3C) could allow an unauthenticated, adjacent attacker to trigger a denial of service (DoS) condition.
This vulnerability is due to improper memory management when Cisco IOS XE Software is processing Address Resolution Protocol (ARP) messages. An attacker could exploit this vulnerability by sending crafted ARP messages at a high rate over a period of time to an affected device. A successful exploit could allow the attacker to exhaust system resources, which eventually triggers a reload of the active route switch processor (RSP). If a redundant RSP is not present, the router reloads.
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Analysis
by VulDB Data Team • 08/05/2025
This vulnerability exists within Cisco IOS XE Software running on Cisco ASR 903 Aggregation Services Routers equipped with Route Switch Processor 3 (RSP3C). The flaw specifically manifests in the Cisco Express Forwarding implementation where the software fails to properly manage memory allocation when processing Address Resolution Protocol messages. This memory management deficiency creates a condition where system resources can be systematically depleted through targeted exploitation. The vulnerability is classified as a denial of service issue that can be triggered by an unauthenticated attacker who is physically adjacent to the affected router, making it a local privilege escalation risk within the network infrastructure.
The technical exploitation mechanism relies on sending crafted ARP messages at high frequency rates over extended periods. This sustained attack pattern allows the malicious actor to consume available memory resources within the router's routing processor, ultimately leading to system resource exhaustion. The memory management failure occurs during the processing of ARP packets, where the system does not adequately validate or limit the memory consumption associated with these network protocol messages. The vulnerability demonstrates characteristics consistent with CWE-129 Input Validation and CWE-772 Insufficient Resource Management, where improper handling of input data leads to resource exhaustion and system instability. According to ATT&CK framework, this vulnerability maps to T1499.004 Network Denial of Service and T1566 Phishing, as the attack requires physical proximity to the target device but can be automated to cause sustained disruption.
The operational impact of this vulnerability extends beyond simple service interruption, as it can result in complete router reloads that disrupt network connectivity for the affected infrastructure. When the active route switch processor experiences memory exhaustion, it triggers an automatic system reload process that can take several minutes to complete. During this reload period, network traffic through the affected router is completely interrupted, potentially causing cascading failures throughout the network topology. The risk is particularly severe in environments where redundant route switch processors are not deployed, as the router becomes completely unavailable during the reload process. Organizations relying on these routers for critical network services face significant operational disruption, as the attack can be executed without requiring authentication credentials or advanced network access privileges, making it a particularly dangerous threat vector for physical security boundaries.
Mitigation strategies should focus on both immediate protective measures and long-term architectural improvements. Network administrators should implement rate limiting on ARP traffic at the router level to prevent excessive processing of malicious ARP messages. Physical security controls must be strengthened to prevent unauthorized adjacent access to critical network infrastructure, as the vulnerability requires proximity to the target device. Cisco recommends applying the latest software patches and updates that address the memory management flaws in the IOS XE software implementation. Network segmentation and monitoring solutions should be deployed to detect unusual ARP traffic patterns that may indicate exploitation attempts. Additionally, organizations should consider implementing redundant route switch processors to ensure high availability during potential reload events, as the absence of redundant hardware significantly increases the operational impact of this vulnerability. The mitigation approach should also include regular network security assessments and vulnerability scanning to identify other potential weaknesses in the network infrastructure that could be exploited in conjunction with this vulnerability.