CVE-2021-1370
📋 TL;DR
This vulnerability allows authenticated local attackers on affected Cisco routers to escalate privileges to root by exploiting insufficient command line argument validation. It affects Cisco IOS XR Software on 8000 Series and NCS540 Series routers running specific NCS540L software images. Attackers need valid device accounts but can then execute crafted commands to gain full system control.
💻 Affected Systems
- Cisco 8000 Series Routers
- Cisco Network Convergence System 540 Series Routers
📦 What is this software?
Ios Xr by Cisco
Ios Xr by Cisco
Ios Xr by Cisco
⚠️ Risk & Real-World Impact
Worst Case
An attacker with low-level credentials gains complete root access, enabling full device compromise, configuration modification, data exfiltration, and persistence establishment.
Likely Case
Malicious insiders or compromised accounts escalate privileges to bypass security controls, modify network configurations, or install backdoors.
If Mitigated
With proper access controls and monitoring, exploitation attempts are detected and contained before significant damage occurs.
🎯 Exploit Status
Exploitation requires authenticated access but involves simple command injection; no public exploit code known
🛠️ 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-iosxr-pe-QpzCAePe
Restart Required: Yes
Instructions:
1. Review Cisco Security Advisory for affected versions. 2. Upgrade to recommended fixed releases. 3. Schedule maintenance window for router restart. 4. Verify patch installation post-upgrade.
🔧 Temporary Workarounds
Restrict CLI Access
allLimit command-line interface access to trusted administrators only using role-based access control
configure terminal
aaa authorization exec default local
aaa authentication login default local
username <admin> privilege 15 secret <password>
Monitor Command Execution
allEnable logging and monitoring of CLI command execution for suspicious activity
logging host <syslog-server>
archive log config logging enable
archive log config notify syslog
🧯 If You Can't Patch
- Implement strict access controls and least privilege principles for all device accounts
- Enable comprehensive logging and monitoring of CLI sessions with alerting for privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check device model and software version: 'show version' and verify if running affected NCS540L imagesCheck Version:
show version | include Cisco IOS XRVerify Fix Applied:
After patching: 1. Run 'show version' to confirm updated release. 2. Test privilege escalation attempts to verify mitigation.📡 Detection & Monitoring
Log Indicators:
- Unusual privilege escalation attempts in system logs
- Multiple failed then successful authentication events from same account
- Commands with unusual arguments or syntax
Network Indicators:
- Unexpected configuration changes
- Unauthorized administrative access patterns
SIEM Query:
source="cisco_ios" AND (event_type="privilege_escalation" OR command="*crafted*" OR user_privilege_change="*root*")