CVE-2021-20165 – This CVE describes a Cross-Site Request Forgery... (How to Fix)

Q: What is the severity of CVE-2021-20165?

CVE-2021-20165 has a CVSS score of 8.8 (HIGH). This CVE describes a Cross-Site Request Forgery (CSRF) vulnerability in Trendnet AC2600 TEW-827DRU routers. Attackers can trick authenticated users into performing unintended actions on the router's web interface, potentially changing settings or compromising the device. This affects users of the vulnerable router firmware version.

📋 TL;DR

This CVE describes a Cross-Site Request Forgery (CSRF) vulnerability in Trendnet AC2600 TEW-827DRU routers. Attackers can trick authenticated users into performing unintended actions on the router's web interface, potentially changing settings or compromising the device. This affects users of the vulnerable router firmware version.

💻 Affected Systems

Products:

Trendnet AC2600 TEW-827DRU

Versions: 2.08B01

Operating Systems: Router firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Affects web management interface. Requires attacker to lure authenticated user to malicious site.

📦 What is this software?

Tew 827dru Firmware by Trendnet

View all CVEs affecting Tew 827dru Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete router compromise allowing attacker to change DNS settings, enable remote administration, steal credentials, or brick the device.

🟠

Likely Case

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

🟢

If Mitigated

Limited impact with proper network segmentation and user awareness training.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires user interaction but CSRF bypass is trivial. Tenable research provides technical details.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Check Trendnet for latest firmware

Vendor Advisory: https://www.trendnet.com/support/

Restart Required: Yes

Instructions:

1. Log into Trendnet support portal. 2. Download latest firmware for TEW-827DRU. 3. Upload via router web interface. 4. Reboot router.

🔧 Temporary Workarounds

Network Segmentation

all

Isolate router management interface from user networks

Browser CSRF Protection

all

Use browser extensions that detect CSRF attempts

🧯 If You Can't Patch

Disable remote management and only access router from trusted internal network
Implement strict same-origin policies and use anti-CSRF browser extensions

🔍 How to Verify

Check if Vulnerable:

Check router firmware version in web interface under Administration > Firmware

Check Version:

Login to router web interface and navigate to firmware section

Verify Fix Applied:

Verify firmware version is newer than 2.08B01 and test CSRF token validation

📡 Detection & Monitoring

Log Indicators:

Multiple configuration changes from same IP in short time
Unexpected POST requests to router endpoints

Network Indicators:

Cross-origin requests to router management interface
Suspicious referrer headers

SIEM Query:

source="router_logs" AND (action="config_change" OR uri="/apply.cgi") AND count() > 5 within 1m

📊 Metadata

CVE ID: CVE-2021-20165

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: December 30, 2021

Last Updated: November 21, 2024

🔗 References

https://www.tenable.com/security/research/tra-2021-54 Exploit,Third Party Advisory
https://www.tenable.com/security/research/tra-2021-54 Exploit,Third Party Advisory

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🔗 Related Vulnerabilities

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