Cisco has issued a warning about a critical zero-day vulnerability in its IOS XE Software (CVE-2023-20198) that’s currently being actively exploited by attackers. The flaw allows attackers to gain full administrator privileges, potentially taking complete control of routers. The vulnerability specifically impacts devices with the Web User Interface (Web UI) feature enabled and the HTTP or HTTPS Server feature toggled on.
Attackers are able to create privileged accounts, granting them full control over the compromised device. Cisco has advised administrators to disable the HTTP server feature on internet-facing systems to mitigate the risk and recommends monitoring for unusual user accounts.
The attacks were first discovered by Cisco’s Technical Assistance Center (TAC) on September 28, prompted by reports of unusual behavior on a customer’s device. Further investigation revealed related activity dating back to September 18, where an authorized user created a local user account with the username “cisco_tac_admin” from a suspicious IP address.
Additional related activity on October 12 involved the creation of a “cisco_support” local user account from a second suspicious IP address. Malicious implants were also deployed to execute arbitrary commands at the system or IOS levels. Cisco assesses that these clusters of activity were likely carried out by the same actor, suggesting an expansion of their operation from the initial testing.
To mitigate the vulnerability, Cisco strongly recommends disabling the HTTP Server feature on all internet-facing systems using specific commands. Administrators should also check for unexplained or recently created user accounts, which could be indicators of malicious activity.
Cisco is working to provide a software fix and urges immediate action as outlined in the security advisory. In the past month, Cisco has cautioned customers about another zero-day vulnerability (CVE-2023-20109) in its IOS and IOS XE software, which was also targeted by attackers.