CVE-2021-1340 – This vulnerability allows authenticated remote ... (How to Fix)

Q: What is the severity of CVE-2021-1340?

CVE-2021-1340 has a CVSS score of 7.2 (HIGH). This vulnerability allows authenticated remote attackers to execute arbitrary code as root or cause denial of service on affected Cisco Small Business routers. Attackers need valid administrator credentials to exploit improper input validation in the web management interface. Organizations using these specific router models are affected.

📋 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 need valid administrator credentials to exploit improper input validation in the web management interface. Organizations using these specific router models are affected.

💻 Affected Systems

Products:

Cisco Small Business RV016
RV042
RV042G
RV082
RV320
RV325 Routers

Versions: All versions prior to the fixed releases

Operating Systems: Embedded router OS

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations with web management enabled are vulnerable. Requires authenticated access.

📦 What is this software?

⚠️ 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 for connected users and services.

🟢

If Mitigated

Limited impact if strong credential management and network segmentation prevent unauthorized access to management interfaces.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires valid administrator credentials and crafting specific HTTP requests to the web interface.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: RV016: 4.2.3.14, RV042/RV042G: 4.2.3.14, RV082: 4.2.3.14, RV320/RV325: 1.5.1.11

Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-rv-overflow-ghZP68yj

Restart Required: Yes

Instructions:

1. Log into router web interface. 2. Navigate to Administration > Firmware Upgrade. 3. Download appropriate firmware from Cisco website. 4. Upload and install firmware. 5. Router will reboot automatically.

🔧 Temporary Workarounds

Restrict Management Access

all

Limit 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

all

Use alternative management methods like CLI or disable web interface if not needed

Disable HTTP/HTTPS management via router configuration

🧯 If You Can't Patch

Implement strict network segmentation to isolate router management interfaces
Enforce strong password policies and multi-factor authentication for router admin accounts

🔍 How to Verify

Check if Vulnerable:

Check router firmware version via web interface: Status > Router > Firmware Version

Check Version:

Check via web interface or SSH: show version

Verify Fix Applied:

Confirm firmware version matches or exceeds patched versions listed in vendor advisory

📡 Detection & Monitoring

Log Indicators:

Multiple failed authentication attempts followed by successful login and unusual HTTP requests
Router reboot logs without scheduled maintenance

Network Indicators:

Unusual HTTP POST requests to router management interface
Traffic patterns suggesting router configuration changes

SIEM Query:

source="router_logs" (event="authentication_success" AND user="admin") AND (url="*cgi*" OR url="*php*" OR method="POST")

📊 Metadata

CVE ID: CVE-2021-1340

CVSS v3 Score: 7.2 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-121

Published: February 4, 2021

Last Updated: November 21, 2024

🔗 References

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