What Happened
The FBI and CISA have issued a joint advisory warning that attackers are actively exploiting a critical zero-day vulnerability in Cisco’s IOS and IOS XE software. The flaw, tracked as CVE-2018-0171, allows unauthenticated remote attackers to gain full administrative control of vulnerable Cisco devices.
Exploitation has already been observed in the wild, where adversaries are deploying webshells on compromised routers and switches to maintain persistence and issue arbitrary commands. Cisco Talos has confirmed hundreds of devices have been impacted globally.
Why It Matters
Both IOS and IOS XE software from Cisco powers core networking equipment for enterprises, service providers, government agencies, and critical infrastructure operators. These devices sit at the heart of IT environments, managing traffic flow, enforcing segmentation, and controlling access.
If attackers gain control of routers and switches, they gain control of the entire network’s trust foundation. This risk goes far beyond downtime, it directly impacts:
- Confidentiality: Attackers can intercept or reroute sensitive data.
- Integrity: Configuration changes allow malicious redirection, credential theft, or lateral movement.
- Availability: Adversaries can disrupt routing and firewalling, leading to outages.
How the Exploit Works
Cisco has confirmed that attackers are:
- Sending crafted HTTP requests to affected devices.
- Creating unauthorized privileged admin accounts without authentication.
- Deploying webshell backdoors, which allow persistent command execution even after device restarts.
- Using these footholds to maintain covert long-term access.
In some cases, the attacker’s persistence has survived device reboots and firmware changes; making post-compromise cleanup extremely difficult without a full rebuild and credential reset.
Risks to Organizations
The implications of this vulnerability are severe:
- Network compromise: complete control of edge devices, allowing attackers to monitor and manipulate traffic.
- Credential theft: harvesting of administrator credentials, enabling deeper intrusions.
- Espionage & data exfiltration: covert long-term access to sensitive information.
- Ransomware staging: compromised routers provide a launchpad for broader attacks.
Organizations that rely heavily on Cisco for perimeter and core routing are particularly vulnerable. This incident highlights the need for a proactive defense strategy around network infrastructure, rather than just focusing on endpoints and applications.
Next Steps
Security agencies and Cisco strongly recommend treating this threat as high priority. To get ahead of similar exploits, defenders should:
- Apply Cisco’s latest security updates and mitigations without delay.
- Audit for unauthorized accounts and unusual configuration changes that may indicate persistence.
- Include routers and firewalls in penetration testing to close high-impact gaps.
- Review logs and continuously monitor for anomalous activity tied to webshells or credential use.
- Tighten access controls by rotating network administrator credentials to reduce the impact of compromise.
- Stay up to date on advisories and white papers to track early warnings and emerging risks.
- Validate incident response readiness to ensure quick reactions to infrastructure-level compromises.
By addressing this Cisco IOS and IOS XE flaw swiftly and adopting a layered security approach, organizations can reduce the risk of long-term infiltration and ensure their network infrastructure remains trustworthy.
