CVE-2018-18555
📋 TL;DR
CVE-2018-18555 is a sandbox escape vulnerability in VyOS that allows authenticated operator users to break out of the restricted management shell and execute arbitrary operating system commands. This affects VyOS 1.1.8 installations where operator-level accounts exist. Attackers can gain elevated privileges on the underlying Linux system.
💻 Affected Systems
- VyOS
📦 What is this software?
Vyos by Vyos
⚠️ Risk & Real-World Impact
Worst Case
An authenticated operator user gains full root access to the underlying Linux system, enabling complete device compromise, data exfiltration, network pivoting, and persistent backdoor installation.
Likely Case
An authenticated malicious operator or compromised operator account executes arbitrary commands with elevated privileges, potentially disrupting network services or stealing configuration data.
If Mitigated
With proper access controls and monitoring, exploitation would be detected and contained, limiting impact to isolated network segments.
🎯 Exploit Status
Exploitation requires authenticated operator access. The vulnerability involves using shell special characters to escape the restricted shell environment.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 1.1.8 with operator level removed (1.2.0 and later)
Vendor Advisory: https://blog.vyos.io/the-operator-level-is-proved-insecure-and-will-be-removed-in-the-next-releases
Restart Required: No
Instructions:
1. Upgrade VyOS to version 1.2.0 or later where operator level has been completely removed. 2. Alternatively, remove all operator-level user accounts and convert them to admin-level accounts if upgrading isn't immediately possible.
🔧 Temporary Workarounds
Remove operator-level accounts
linuxDelete or disable all operator-level user accounts to eliminate the attack vector
delete system login user [username] level operator
commit
save
Restrict operator command access
linuxLimit available commands for operator users through configuration restrictions
set system login user [username] authentication encrypted-password [hash]
set system login user [username] level admin
commit
save
🧯 If You Can't Patch
- Immediately remove all operator-level user accounts and use only admin-level accounts
- Implement strict network segmentation to isolate VyOS devices from critical infrastructure
🔍 How to Verify
Check if Vulnerable:
Check if operator-level users exist: show configuration commands | match 'level operator'Check Version:
show versionVerify Fix Applied:
Verify no operator-level users exist and system is running VyOS 1.2.0 or later📡 Detection & Monitoring
Log Indicators:
- Unusual command sequences from operator accounts
- Shell escape characters in command logs
- Unexpected process execution from operator sessions
Network Indicators:
- Unusual outbound connections from VyOS management interface
- SSH/Telnet sessions with command injection patterns
SIEM Query:
source="vyos*" ("operator" AND ("$" OR "|" OR ";" OR "`"))