CVE-2021-1338
📋 TL;DR
This vulnerability allows authenticated remote attackers to execute arbitrary code as root or cause denial of service on affected Cisco Small Business routers. It affects routers with web-based management interfaces due to improper input validation. Attackers need valid administrator credentials to exploit it.
💻 Affected Systems
- Cisco Small Business RV016
- RV042
- RV042G
- RV082
- RV320
- RV325 Routers
📦 What is this software?
Rv016 Multi Wan Vpn Router Firmware by Cisco
View all CVEs affecting Rv016 Multi Wan Vpn Router Firmware →
Rv042 Dual Wan Vpn Router Firmware by Cisco
View all CVEs affecting Rv042 Dual Wan Vpn Router Firmware →
Rv042g Dual Gigabit Wan Vpn Router Firmware by Cisco
View all CVEs affecting Rv042g Dual Gigabit Wan Vpn Router Firmware →
Rv082 Dual Wan Vpn Router Firmware by Cisco
View all CVEs affecting Rv082 Dual Wan Vpn Router Firmware →
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with root-level arbitrary code execution, leading to data theft, network manipulation, or persistent backdoor installation.
Likely Case
Denial of service from device reboots, disrupting network connectivity and business operations.
If Mitigated
Limited to authenticated users with strong credentials; impact reduced to potential DoS if patched or isolated.
🎯 Exploit Status
Exploitation requires authenticated access; complexity is low once credentials are obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco advisory for specific fixed versions per model.
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-rv-overflow-ghZP68yj
Restart Required: Yes
Instructions:
1. Access router web interface. 2. Navigate to firmware update section. 3. Download and apply latest firmware from Cisco. 4. Reboot router after update.
🔧 Temporary Workarounds
Disable Web Management Interface
allTurn off the web-based management interface to prevent exploitation via HTTP requests.
Access router CLI or web interface, navigate to management settings, disable web management.
Restrict Access with ACLs
allUse access control lists to limit web interface access to trusted IP addresses only.
Configure ACLs on router to allow management from specific IPs, e.g., 'access-list 1 permit 192.168.1.0 0.0.0.255'.
🧯 If You Can't Patch
- Enforce strong, unique administrator passwords and use multi-factor authentication if supported.
- Isolate routers on a dedicated management VLAN and monitor for suspicious HTTP traffic.
🔍 How to Verify
Check if Vulnerable:
Check router firmware version against Cisco advisory; if unpatched and web management is enabled, assume vulnerable.Check Version:
Log into router web interface or CLI and run 'show version' or check firmware info in settings.Verify Fix Applied:
Confirm firmware version matches or exceeds patched version listed in Cisco advisory.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests to management interface, multiple failed login attempts followed by crafted requests.
Network Indicators:
- Spikes in HTTP traffic to router management port, unexpected device reboots.
SIEM Query:
source="router_logs" AND (http_request LIKE "%admin%" OR event="reboot")