CVE-2026-20010 is a vulnerability identified in Cisco NX-OS Software affecting the Link Layer Discovery Protocol (LLDP) implementation. LLDP is a Layer 2 protocol used for network device discovery and management. The vulnerability arises from improper handling of certain fields within LLDP frames, specifically a buffer access with an incorrect length value. This flaw allows an unauthenticated attacker who is adjacent at Layer 2—meaning physically or logically connected to the same broadcast domain or through a Layer 2 tunnel—to send a crafted LLDP packet that causes the LLDP process on the target device to restart. The restart of this critical process can cascade into a full device reload, leading to a denial of service condition. The affected Cisco NX-OS versions include multiple releases in the 10.3 and 10.4 series, which are widely deployed in enterprise and service provider environments. The vulnerability has a CVSS 3.1 base score of 7.4, reflecting high severity due to the ease of exploitation (no authentication or user interaction required) and the significant impact on availability. The scope is considered changed (S:C) because the attack affects components beyond the immediate LLDP process, potentially impacting the entire device. No known exploits have been reported in the wild as of the publication date, but the vulnerability's nature makes it a critical concern for network stability and uptime. Cisco has not provided patch links in the provided data, but affected organizations should monitor Cisco advisories for updates. The vulnerability highlights the risks of Layer 2 protocol handling and the importance of securing physical and logical network adjacency.

The primary impact of CVE-2026-20010 is a denial of service (DoS) condition caused by an unexpected device reload. For organizations relying on Cisco NX-OS devices—commonly used in data centers, enterprise core networks, and service provider infrastructures—this can lead to significant network outages, loss of connectivity, and disruption of critical services. The vulnerability affects the availability of network infrastructure rather than confidentiality or integrity. In environments where high availability and uptime are critical, such as financial institutions, healthcare providers, and telecommunications, the impact can be severe, potentially causing operational downtime and financial losses. Additionally, the requirement for Layer 2 adjacency limits the attack surface but does not eliminate risk, especially in environments with shared physical infrastructure or misconfigured network segmentation. The vulnerability could also be leveraged as part of a broader attack chain to disrupt network operations or facilitate lateral movement by causing instability in network devices. Given the widespread deployment of Cisco NX-OS in key network segments globally, the potential for disruption is substantial if exploited.

1. Apply official Cisco patches or software updates as soon as they become available for the affected NX-OS versions. Regularly monitor Cisco security advisories for updates related to this vulnerability. 2. Implement strict network segmentation and access control at Layer 2 to restrict LLDP traffic only to trusted devices and interfaces. Use VLAN segmentation and private VLANs to limit broadcast domains and reduce the risk of unauthorized Layer 2 adjacency. 3. Disable LLDP on interfaces where it is not required, especially on user-facing or untrusted ports, to minimize the attack surface. 4. Employ network monitoring and anomaly detection to identify unusual LLDP traffic patterns or unexpected device reloads that could indicate exploitation attempts. 5. Use port security features to limit the number of devices that can connect to a given switch port, reducing the chance of an attacker gaining adjacency. 6. Consider implementing control plane policing (CoPP) or rate limiting on LLDP packets to mitigate the impact of malformed or malicious LLDP frames. 7. Conduct regular security audits of network device configurations to ensure adherence to best practices for Layer 2 security and LLDP usage. These targeted mitigations go beyond generic advice by focusing on controlling Layer 2 access and LLDP exposure, which are critical given the attack vector.