CVE-2021-31326 – This vulnerability allows unauthenticated attac... (How to Fix)

Q: What is the severity of CVE-2021-31326?

CVE-2021-31326 has a CVSS score of 9.8 (CRITICAL). This vulnerability allows unauthenticated attackers to remotely reset D-Link DIR-816 A2 routers to factory defaults via a crafted HTTP request. Attackers can exploit this by sending a specially crafted tokenid parameter to the /goform/form2Reboot.cgi endpoint. This affects all users of vulnerable D-Link DIR-816 A2 routers with firmware version 1.10 B05.

📋 TL;DR

This vulnerability allows unauthenticated attackers to remotely reset D-Link DIR-816 A2 routers to factory defaults via a crafted HTTP request. Attackers can exploit this by sending a specially crafted tokenid parameter to the /goform/form2Reboot.cgi endpoint. This affects all users of vulnerable D-Link DIR-816 A2 routers with firmware version 1.10 B05.

💻 Affected Systems

Products:

D-Link DIR-816 A2

Versions: Firmware version 1.10 B05

Operating Systems: Embedded router firmware

Default Config Vulnerable: ⚠️ Yes

Notes: All devices running the vulnerable firmware version are affected regardless of configuration.

📦 What is this software?

Dir 816 Firmware by Dlink

View all CVEs affecting Dir 816 Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Attackers can remotely reset the router to factory defaults, disabling all security configurations, changing network settings, and potentially gaining administrative access to the device.

🟠

Likely Case

Attackers cause service disruption by resetting the router, forcing network downtime and requiring manual reconfiguration of all router settings.

🟢

If Mitigated

If the router is not internet-facing and proper network segmentation is in place, the impact is limited to potential internal network disruption.

🌐 Internet-Facing: HIGH - The vulnerability is remotely exploitable without authentication, making internet-facing routers extremely vulnerable to disruption attacks.

🏢 Internal Only: MEDIUM - Internal attackers or malware on the local network could exploit this to cause network disruption and potentially gain router access.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

The exploit requires only a single HTTP request with a crafted parameter, making it trivial to weaponize.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Check D-Link support for latest firmware

Vendor Advisory: https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10240

Restart Required: Yes

Instructions:

1. Log into D-Link support portal. 2. Download latest firmware for DIR-816 A2. 3. Access router admin interface. 4. Navigate to firmware update section. 5. Upload and apply new firmware. 6. Router will reboot automatically.

🔧 Temporary Workarounds

Block access to vulnerable endpoint

linux

Use firewall rules to block external access to /goform/form2Reboot.cgi

iptables -A INPUT -p tcp --dport 80 -m string --string "/goform/form2Reboot.cgi" --algo bm -j DROP
iptables -A INPUT -p tcp --dport 443 -m string --string "/goform/form2Reboot.cgi" --algo bm -j DROP

Disable remote administration

all

Turn off remote management feature in router settings

🧯 If You Can't Patch

Place router behind a firewall that blocks all inbound WAN traffic to router management interface
Change default admin credentials and implement strong authentication

🔍 How to Verify

Check if Vulnerable:

Check router firmware version in admin interface. If version is 1.10 B05, the device is vulnerable.

Check Version:

curl -s http://router-ip/ | grep -i firmware || Check router admin interface System Status page

Verify Fix Applied:

After firmware update, verify version has changed from 1.10 B05 to a newer version.

📡 Detection & Monitoring

Log Indicators:

HTTP requests to /goform/form2Reboot.cgi with tokenid parameter
Router reboot events in system logs
Factory reset events

Network Indicators:

HTTP POST requests to router IP on port 80/443 with form2Reboot.cgi in URL
Unusual traffic patterns to router management interface

SIEM Query:

source="router.log" AND (url="/goform/form2Reboot.cgi" OR event="reboot" OR event="factory_reset")

📊 Metadata

CVE ID: CVE-2021-31326

CVSS v3 Score: 9.8 (CRITICAL)

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

CWE: CWE-287

Published: March 24, 2022

Last Updated: November 21, 2024

🔗 References

https://github.com/GD008/vuln/blob/main/DIR-816_reset.md Exploit,Third Party Advisory
https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10240 Vendor Advisory
https://www.dlink.com/en/security-bulletin/ Vendor Advisory
https://github.com/GD008/vuln/blob/main/DIR-816_reset.md Exploit,Third Party Advisory
https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10240 Vendor Advisory
https://www.dlink.com/en/security-bulletin/ Vendor Advisory

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