CVE-2021-3229 – CVE-2021-3229 is a denial-of-service vulnerabil... (How to Fix)

Q: What is the severity of CVE-2021-3229?

CVE-2021-3229 has a CVSS score of 7.5 (HIGH). CVE-2021-3229 is a denial-of-service vulnerability in ASUS RT-AX3000 router firmware that allows an attacker to disrupt device setup services through continuous login attempts. This affects users of ASUSWRT firmware versions 3.0.0.4.384_10177 and earlier. The vulnerability prevents legitimate users from accessing router configuration interfaces.

📋 TL;DR

CVE-2021-3229 is a denial-of-service vulnerability in ASUS RT-AX3000 router firmware that allows an attacker to disrupt device setup services through continuous login attempts. This affects users of ASUSWRT firmware versions 3.0.0.4.384_10177 and earlier. The vulnerability prevents legitimate users from accessing router configuration interfaces.

💻 Affected Systems

Products:

ASUS RT-AX3000

Versions: 3.0.0.4.384_10177 and earlier

Operating Systems: ASUSWRT firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Affects the web administration interface of the router.

📦 What is this software?

Rt Ax3000 Firmware by Asus

View all CVEs affecting Rt Ax3000 Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Router becomes completely inaccessible for configuration, requiring physical reset and potential loss of custom settings.

🟠

Likely Case

Temporary disruption of web interface access until attack stops or router is rebooted.

🟢

If Mitigated

Minimal impact with proper network segmentation and access controls.

🌐 Internet-Facing: HIGH - Routers are typically internet-facing and vulnerable to remote attacks.

🏢 Internal Only: MEDIUM - Could be exploited by malicious internal users or compromised devices.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Simple script available on GitHub demonstrates continuous login attempts to trigger DoS.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Versions after 3.0.0.4.384_10177

Vendor Advisory: https://www.asus.com/us/ASUSWRT/

Restart Required: Yes

Instructions:

1. Log into router web interface. 2. Navigate to Administration > Firmware Upgrade. 3. Check for updates. 4. Download and install latest firmware. 5. Reboot router after installation.

🔧 Temporary Workarounds

Disable Remote Administration

all

Prevent external access to router administration interface

Implement Rate Limiting

all

Configure firewall rules to limit login attempts per IP

🧯 If You Can't Patch

Place router behind additional firewall with strict access controls
Disable WAN access to administration interface and use VPN for remote management

🔍 How to Verify

Check if Vulnerable:

Check firmware version in router web interface under Administration > Firmware Upgrade

Check Version:

Not applicable - check via web interface

Verify Fix Applied:

Confirm firmware version is newer than 3.0.0.4.384_10177

📡 Detection & Monitoring

Log Indicators:

Multiple failed login attempts from single IP
Web interface becoming unresponsive

Network Indicators:

High volume of HTTP POST requests to login endpoint
Unusual traffic patterns to router administration port

SIEM Query:

source_ip="router_ip" AND (event_type="failed_login" COUNT > 10 WITHIN 1min)

📊 Metadata

CVE ID: CVE-2021-3229

CVSS v3 Score: 7.5 (HIGH)

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

Published: February 5, 2021

Last Updated: November 21, 2024

🔗 References

https://dlcdnimgs.asus.com/websites/global/productcustomizedTab/562/ASUSWRT%20portal%20feature.pdf Product,Vendor Advisory
https://github.com/fullbbadda1208/CVE-2021-3229 Exploit,Third Party Advisory
https://www.asus.com/us/ASUSWRT/ Product,Vendor Advisory
https://dlcdnimgs.asus.com/websites/global/productcustomizedTab/562/ASUSWRT%20portal%20feature.pdf Product,Vendor Advisory
https://github.com/fullbbadda1208/CVE-2021-3229 Exploit,Third Party Advisory
https://www.asus.com/us/ASUSWRT/ Product,Vendor Advisory

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