A vulnerability in the Image Verification feature of Cisco IOS XE Software could allow an authenticated, local attacker to install a malicious software image or file on an affected device. The vulnerability is due to the affected software improperly verifying digital signatures for software images and files that are uploaded to a device. An attacker could exploit this vulnerability by uploading a malicious software image or file to an affected device. A successful exploit could allow the attacker to bypass digital signature verification checks for software images and files and install a malicious software image or file on the affected device.
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180926-digsig