CVE-2026-20173 in NX-OS Software
Summary
by MITRE • 10/07/2026
A vulnerability in Cisco NX-OS Software could allow an unauthenticated, remote attacker to exhaust system resources, causing a denial of service (DoS) condition.
This vulnerability exists because rate limiting was improperly applied to some protocols. An attacker could exploit this vulnerability by sending a high rate of UDP or TCP connections to a data plane interface on an affected device. A successful exploit could allow the attacker to cause instability to various routing and control plane protocols through some packet loss and temporary disruptions, causing a DoS condition. This DoS condition will clear without manual intervention soon after the high rate of traffic is stopped.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified in Cisco NX-OS Software represents a significant risk to network infrastructure stability due to improper implementation of rate limiting mechanisms for specific protocols. As a cyber security specialist with two decades of experience, it is critical to understand that this flaw allows an unauthenticated, remote attacker to trigger a denial of service condition by exploiting the data plane interface. The core technical issue lies in the failure of the operating system to adequately constrain incoming traffic volumes from certain protocol types, specifically UDP and TCP connections. When an adversary sends a high rate of these connection attempts against an affected device, the system fails to drop or throttle excess packets effectively, leading to resource exhaustion within the control plane components responsible for managing routing tables and network state information.
From a technical perspective, this vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, which describes scenarios where a software application does not properly limit the amount of resources it consumes during normal operation or in response to specific inputs. The attack vector involves flooding the data plane with excessive UDP or TCP connection requests. Because NX-OS relies on these control plane processes to maintain routing integrity and network connectivity, the influx of unthrottled packets causes CPU spikes and memory pressure that degrade system performance. This results in packet loss for legitimate traffic and temporary disruptions to critical routing protocols such as OSPF, BGP, or EIGRP, which depend on consistent processing cycles to exchange updates and maintain neighbor adjacencies.
The operational impact of this vulnerability is severe but transient. A successful exploitation leads to a denial of service condition characterized by instability in various routing and control plane functions. Network administrators may observe intermittent connectivity issues, increased latency, or complete loss of management access during the attack window. However, unlike persistent vulnerabilities that require manual remediation after an incident, this specific flaw exhibits self-healing properties. The DoS condition clears automatically without manual intervention shortly after the high-rate traffic source is stopped. This characteristic suggests that while the vulnerability can cause significant disruption in real-time, it does not typically result in permanent system compromise or data loss once the attack ceases, although repeated attacks could lead to hardware fatigue or configuration drift over time.
In terms of industry standard mapping, this incident aligns with MITRE ATT&CK technique T1498: Network Denial of Service, specifically sub-technique T1498.002: Volumetric Floods. The attacker utilizes volumetric pressure to overwhelm the target's capacity rather than exploiting a logic flaw in authentication or authorization mechanisms directly. To mitigate this risk, network operators should implement strict ingress filtering and rate limiting policies at the perimeter of their networks using access control lists (ACLs) or dedicated DDoS mitigation appliances before traffic reaches the NX-OS devices. Additionally, enabling TCP SYN cookies if applicable to the specific protocol versions can help manage connection state resources more effectively. Cisco has likely released software updates that correct the rate-limiting logic for these protocols; therefore, applying the latest recommended firmware patches is essential to close this gap in network defense posture and ensure resilience against resource exhaustion attacks.