CVE-2021-1324 – This vulnerability allows authenticated remote ... (How to Fix)

Q: What is the severity of CVE-2021-1324?

CVE-2021-1324 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 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.

📋 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

Products:

Cisco Small Business RV016
Cisco Small Business RV042
Cisco Small Business RV042G
Cisco Small Business RV082
Cisco Small Business RV320
Cisco Small Business RV325

Versions: All versions prior to the fixed releases

Operating Systems: Embedded router OS

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations are vulnerable. The web management interface is typically enabled by default on these devices.

📦 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, network traffic interception, and lateral movement to connected systems.

🟠

Likely Case

Denial of service through device reboots disrupting network connectivity, potentially combined with limited code execution for persistence or reconnaissance.

🟢

If Mitigated

No impact if proper credential management and network segmentation prevent attackers from reaching the management interface with valid credentials.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires valid administrator credentials but is technically simple once credentials are obtained. The vulnerability is in the web interface accessible over HTTP/HTTPS.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: RV016: 4.2.3.14, RV042/RV042G: 4.2.3.14, RV082: 4.2.3.14, RV320: 1.5.1.11, 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 the router web interface. 2. Navigate to Administration > Firmware Upgrade. 3. Download the appropriate firmware from Cisco's support site. 4. Upload and install the firmware. 5. The router will reboot automatically after installation.

🔧 Temporary Workarounds

Disable Web Management Interface

all

Disable the web-based management interface and use CLI or other management methods if available

Restrict Management Access

all

Configure firewall rules to restrict access to the management interface to trusted IP addresses only

🧯 If You Can't Patch

Implement strict credential management with strong, unique passwords and multi-factor authentication if supported
Segment the management interface to a dedicated VLAN with strict access controls and monitoring

🔍 How to Verify

Check if Vulnerable:

Check the firmware version in the router web interface under Status > Router > Firmware Version

Check Version:

No CLI command available; must check via web interface at Status > Router > Firmware Version

Verify Fix Applied:

Verify the firmware version matches or exceeds the patched versions listed in the vendor advisory

📡 Detection & Monitoring

Log Indicators:

Multiple failed login attempts followed by successful login and unusual HTTP requests to management endpoints
Device reboot logs without scheduled maintenance

Network Indicators:

Unusual HTTP POST requests to router management interface from unexpected sources
Traffic patterns suggesting device reboots or configuration changes

SIEM Query:

source="router_logs" AND (event_type="authentication" AND result="success" AND user="admin") FOLLOWED BY (event_type="http_request" AND uri CONTAINS "/apply.cgi" OR uri CONTAINS "/login.cgi") WITHIN 5 minutes

📊 Metadata

CVE ID: CVE-2021-1324

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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