CVE-2021-1326
📋 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 administrator credentials can exploit improper input validation in the web management interface via crafted HTTP requests. Organizations using these specific router models are affected.
💻 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
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 limited code execution if attackers have sophisticated capabilities.
If Mitigated
No impact if proper access controls prevent unauthorized administrative access and the vulnerability is patched.
🎯 Exploit Status
Requires valid administrator credentials, making exploitation more difficult but still dangerous for compromised accounts.
🛠️ 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 Administrative Access
allLimit web management interface access to trusted IP addresses only
Configure firewall rules to restrict access to router management IP/port from specific source IPs
Disable Web Management Interface
allUse alternative management methods if web interface is not required
Disable HTTP/HTTPS management in router configuration
🧯 If You Can't Patch
- Implement strict network segmentation to isolate routers from critical systems
- Enforce strong password policies and multi-factor authentication for administrative accounts
🔍 How to Verify
Check if Vulnerable:
Check router firmware version against Cisco advisory and compare with fixed versions listedCheck Version:
Log into web interface and check System Summary or Status page for firmware versionVerify Fix Applied:
Confirm firmware version matches or exceeds fixed version listed in Cisco advisory📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts followed by successful admin login
- Unusual HTTP POST requests to management interface
- Device reboot logs without scheduled maintenance
Network Indicators:
- HTTP traffic to router management interface from unexpected sources
- Unusual outbound connections from router after management interface access
SIEM Query:
source_ip=router_management_interface AND (http_method=POST AND (uri_contains="cgi" OR uri_contains="admin")) AND status_code=200