Cisco IOS is a monolithic operating system running directly on the hardware while IOS XE is a combination of a linux kernel and a (monolithic) application (IOSd) that runs on top of this kernel. Attacker executing code remotely using system vulnerabilities. It is common type of attack and hard to avoid.

CVE-2018-0151 – Cisco IOS and IOS XE Software Quality of Service Remote Code Execution Vulnerability

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-qos

CVE-2018-0171 – Cisco IOS and IOS XE Software Smart Install Remote Code Execution Vulnerability

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-smi2

CVE-2018-0150 – Cisco IOS XE Software Static Credential Vulnerability

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-xesc