CVE-2021-1336
📋 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. Attackers with valid administrator credentials can exploit improper input validation in the web management interface via crafted HTTP requests. Organizations using Cisco RV016, RV042, RV042G, RV082, RV320, or RV325 routers are affected.
💻 Affected Systems
- Cisco RV016
- Cisco RV042
- Cisco RV042G
- Cisco RV082
- Cisco RV320
- Cisco RV325
📦 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
Complete device compromise with root-level arbitrary code execution, allowing full control of the router and potential lateral movement into connected networks.
Likely Case
Denial of service through device reboots disrupting network connectivity, with potential for authenticated attackers to execute limited code.
If Mitigated
Minimal impact if strong authentication controls prevent unauthorized access to admin credentials and web interface is not exposed externally.
🎯 Exploit Status
Exploitation requires valid administrator credentials. The vulnerability involves stack-based buffer overflow (CWE-121).
🛠️ 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 with admin credentials. 2. Navigate to Administration > Firmware Upgrade. 3. Download appropriate firmware from Cisco support site. 4. Upload and install firmware. 5. Reboot router after installation.
🔧 Temporary Workarounds
Restrict Web Interface Access
allLimit access to the web-based management interface to trusted IP addresses only
Configure firewall rules to restrict access to router management IP/ports
Disable Remote Management
allDisable web management interface from WAN/external interfaces
In router settings: Administration > Management > Disable 'Remote Management'
🧯 If You Can't Patch
- Implement strict network segmentation to isolate affected routers from critical assets
- Enforce strong password policies and multi-factor authentication for admin accounts
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via web interface: Status > Router > Firmware VersionCheck Version:
Via web interface or CLI: show versionVerify Fix Applied:
Verify firmware version matches or exceeds fixed versions listed in Cisco advisory📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by successful login
- Unusual HTTP POST requests to management interface endpoints
- Router reboot logs without scheduled maintenance
Network Indicators:
- Unusual outbound connections from router after admin login
- HTTP traffic patterns matching exploit payloads
SIEM Query:
source="router_logs" AND (event="authentication_success" OR event="reboot") | stats count by src_ip