CVE-2026-20048 is a vulnerability identified in the Simple Network Management Protocol (SNMP) subsystem of Cisco Nexus 9000 Series Fabric Switches operating in Application Centric Infrastructure (ACI) mode. The root cause is improper processing of SNMP requests, specifically when parsing queries to a particular Management Information Base (MIB). This improper handling leads to uncontrolled memory allocation, which can cause a kernel panic and force the device to reload, resulting in a denial of service (DoS) condition. The vulnerability affects a broad range of NX-OS software versions, spanning from 15.2(1g) through 16.1(4h), indicating a long-standing issue across multiple releases. Exploitation requires authentication: for SNMPv1 and SNMPv2c, a valid read-only community string is necessary, while SNMPv3 exploitation demands valid user credentials. The attack vector is network-based with low complexity and no user interaction required, but it requires privileges to access SNMP. The vulnerability impacts availability exclusively, with no direct impact on confidentiality or integrity. Cisco has not reported any known exploits in the wild as of the publication date. This vulnerability is rated with a CVSS v3.1 score of 7.7, reflecting high severity due to the potential for widespread disruption in critical network infrastructure. The issue underscores the risks associated with SNMP exposure and the importance of secure credential management and access controls in network device management.

The primary impact of CVE-2026-20048 is a denial of service condition on Cisco Nexus 9000 Series Fabric Switches operating in ACI mode. A successful exploit causes a kernel panic and forces the device to reload, leading to temporary loss of network connectivity and disruption of data center or enterprise network operations. Given the critical role of Nexus 9000 switches in data center fabrics and ACI deployments, this can result in significant operational downtime, affecting business continuity and potentially causing cascading failures in dependent systems. The vulnerability does not allow data exfiltration or modification, so confidentiality and integrity remain intact. However, the loss of availability in core network infrastructure can impact cloud services, enterprise applications, and critical communications. Organizations relying heavily on Cisco ACI for network automation and segmentation may face increased risk of service degradation or outages. The requirement for valid SNMP credentials limits exploitation to insiders or attackers who have already compromised SNMP authentication, but this does not eliminate the risk, especially in environments with weak SNMP credential management or exposed SNMP interfaces.

1. Apply Cisco's security patches or software updates for NX-OS versions addressing this vulnerability as soon as they become available. 2. Restrict SNMP access strictly to trusted management stations and networks using access control lists (ACLs) and firewall rules to minimize exposure. 3. Enforce strong SNMP authentication by using SNMPv3 with robust user credentials and disable SNMPv1 and SNMPv2c where possible. 4. Regularly audit SNMP community strings and user accounts to ensure they are complex, unique, and rotated periodically. 5. Monitor SNMP traffic for unusual patterns such as repeated queries to specific MIBs that could indicate exploitation attempts. 6. Implement network segmentation to isolate management interfaces from general user networks. 7. Employ intrusion detection/prevention systems (IDS/IPS) capable of detecting anomalous SNMP activity. 8. Conduct regular vulnerability assessments and penetration testing focused on network management protocols. 9. Educate network administrators on secure SNMP configuration and the risks of credential exposure. 10. Maintain up-to-date inventory of affected devices and versions to prioritize remediation efforts effectively.