CVE-2021-20120 – This CVE describes a cross-site request forgery... (How to Fix)

Q: What is the severity of CVE-2021-20120?

CVE-2021-20120 has a CVSS score of 8.8 (HIGH). This CVE describes a cross-site request forgery (CSRF) vulnerability in the Arris Surfboard SB8200 cable modem administration interface. Attackers can trick authenticated users into performing unauthorized configuration changes, including password resets, without their knowledge. All users with the vulnerable modem model are affected.

📋 TL;DR

This CVE describes a cross-site request forgery (CSRF) vulnerability in the Arris Surfboard SB8200 cable modem administration interface. Attackers can trick authenticated users into performing unauthorized configuration changes, including password resets, without their knowledge. All users with the vulnerable modem model are affected.

💻 Affected Systems

Products:

Arris Surfboard SB8200

Versions: All firmware versions prior to fix

Operating Systems: Embedded firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Vulnerability exists in the web administration interface accessible via local network.

📦 What is this software?

Arris Surfboard Sb8200 Firmware by Commscope

View all CVEs affecting Arris Surfboard Sb8200 Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete takeover of the modem with administrative password change, enabling attacker to reconfigure network settings, intercept traffic, or disable the device.

🟠

Likely Case

Unauthorized configuration changes leading to network disruption, DNS hijacking, or credential theft.

🟢

If Mitigated

Limited impact if CSRF protections are implemented or if the admin interface is not accessible.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires the victim to be logged into the admin interface and visit a malicious webpage.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firmware with CSRF protection implemented

Vendor Advisory: https://www.tenable.com/security/research/tra-2021-45

Restart Required: Yes

Instructions:

1. Check current firmware version in admin interface. 2. Contact ISP for firmware update. 3. Apply update via admin interface. 4. Reboot modem after update.

🔧 Temporary Workarounds

Disable remote admin access

all

Prevent external access to admin interface

Access modem admin interface -> Security -> Remote Admin Access -> Disable

Use separate admin browser

all

Use dedicated browser for modem administration only

🧯 If You Can't Patch

Isolate modem on separate VLAN with restricted access
Implement network-level CSRF protection via WAF or proxy

🔍 How to Verify

Check if Vulnerable:

Access admin interface and inspect network requests for CSRF tokens in forms

Check Version:

Access 192.168.100.1 in browser and check firmware version in status page

Verify Fix Applied:

Check if forms include CSRF tokens and verify firmware version

📡 Detection & Monitoring

Log Indicators:

Multiple configuration changes from same IP
Admin password change events

Network Indicators:

HTTP POST requests to admin interface without referrer validation

SIEM Query:

source_ip="192.168.100.1" AND (event_type="config_change" OR event_type="password_change")

📊 Metadata

CVE ID: CVE-2021-20120

CVSS v3 Score: 8.8 (HIGH)

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

CWE: CWE-352

Published: October 21, 2021

Last Updated: November 21, 2024

🔗 References

https://www.tenable.com/security/research/tra-2021-45 Exploit,Third Party Advisory
https://www.tenable.com/security/research/tra-2021-45 Exploit,Third Party Advisory

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