CVE-2020-3403
📋 TL;DR
This vulnerability allows authenticated local attackers with privileged EXEC permissions to inject commands that execute with root privileges upon device reboot. It affects Cisco IOS XE Software due to insufficient protection of startup script values. Attackers can exploit this by writing malicious values to a specific file.
💻 Affected Systems
- Cisco IOS XE Software
📦 What is this software?
Ios Xe by Cisco
Cisco IOS XE is Cisco's modern network operating system running on enterprise routers, switches, and wireless controllers deployed across corporate networks, data centers, branch offices, and service provider infrastructure worldwide. As the evolution of Cisco IOS, IOS XE provides a Linux-based modu...
Learn more about Ios Xe →⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise with persistent root-level command execution after every reboot, allowing full control, data theft, and network manipulation.
Likely Case
Privilege escalation from authenticated user to root, enabling configuration changes, service disruption, and lateral movement within the network.
If Mitigated
Limited impact if proper access controls restrict privileged EXEC permissions and file write access to authorized administrators only.
🎯 Exploit Status
Exploitation requires authenticated access with privileged EXEC permissions and ability to write to specific file.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco Security Advisory for specific fixed releases
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-cmdinj-2MzhjM6K
Restart Required: Yes
Instructions:
1. Check current IOS XE version. 2. Review Cisco Security Advisory for fixed releases. 3. Download and install appropriate fixed software version. 4. Reboot device to apply changes.
🔧 Temporary Workarounds
Restrict Privileged EXEC Access
allLimit privileged EXEC permissions to only necessary administrators using role-based access control.
configure terminal
username <username> privilege <level>
aaa authorization exec default local
end
write memory
Monitor File System Changes
allImplement monitoring for unauthorized writes to startup configuration files and system scripts.
show file systems
show running-config | include logging
configure terminal
logging host <syslog-server>
end
🧯 If You Can't Patch
- Implement strict access controls to limit privileged EXEC permissions to minimum necessary personnel
- Monitor for unauthorized configuration changes and file system modifications, particularly to startup scripts
🔍 How to Verify
Check if Vulnerable:
Check IOS XE version and compare against fixed releases in Cisco Security AdvisoryCheck Version:
show version | include VersionVerify Fix Applied:
Verify installed version matches or exceeds fixed release version from advisory📡 Detection & Monitoring
Log Indicators:
- Unauthorized privileged EXEC access attempts
- Unexpected writes to startup configuration files
- Suspicious commands in configuration changes
Network Indicators:
- Unusual configuration changes from non-standard administrative sources
- Unexpected device reboots or service disruptions
SIEM Query:
source="iosxe" AND (event_type="privileged_access" OR file_write="startup-config" OR command="write")