CVE-2021-33032 – This vulnerability allows unauthenticated remot... (How to Fix)

Q: What is the severity of CVE-2021-33032?

CVE-2021-33032 has a CVSS score of 10.0 (CRITICAL). This vulnerability allows unauthenticated remote attackers to execute arbitrary system commands as root on affected HomeMatic CCU devices via a simple HTTP request to the WebUI component. It affects all CCU2 devices with firmware up to version 2.57.5 and CCU3 devices with firmware up to version 3.57.5. This is a critical vulnerability due to the root-level access and lack of authentication requirements.

📋 TL;DR

This vulnerability allows unauthenticated remote attackers to execute arbitrary system commands as root on affected HomeMatic CCU devices via a simple HTTP request to the WebUI component. It affects all CCU2 devices with firmware up to version 2.57.5 and CCU3 devices with firmware up to version 3.57.5. This is a critical vulnerability due to the root-level access and lack of authentication requirements.

💻 Affected Systems

Products:

eQ-3 HomeMatic CCU2
eQ-3 HomeMatic CCU3

Versions: CCU2 firmware ≤ 2.57.5, CCU3 firmware ≤ 3.57.5

Operating Systems: Embedded Linux (CCU2/CCU3 firmware)

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations are vulnerable. The WebUI component is enabled by default and accessible via HTTP.

📦 What is this software?

Homematic Ccu2 Firmware by Eq 3

View all CVEs affecting Homematic Ccu2 Firmware →

Homematic Ccu3 Firmware by Eq 3

View all CVEs affecting Homematic Ccu3 Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of the HomeMatic central unit, allowing attackers to install persistent backdoors, pivot to other network devices, steal sensitive home automation data, or use the device as part of a botnet.

🟠

Likely Case

Remote attackers gaining full control of the HomeMatic system, potentially manipulating smart home devices (lights, locks, thermostats), stealing personal data, or using the device for cryptocurrency mining.

🟢

If Mitigated

Limited impact if the device is behind a firewall with strict inbound rules and network segmentation, though the vulnerability remains exploitable from internal networks.

🌐 Internet-Facing: HIGH - The WebUI is typically exposed to the internet for remote management, making these devices directly accessible to attackers worldwide.

🏢 Internal Only: HIGH - Even internally, any compromised device or malicious insider can exploit this vulnerability without authentication.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: CONFIRMED

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires only a single HTTP request with crafted parameters. Public proof-of-concept code and detailed analysis are available.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: CCU2: 2.59.7, CCU3: 3.59.6

Vendor Advisory: https://www.eq-3.de/downloads/software/HM-CCU2-Firmware_Updates/HM-CCU-2.59.7/HM-CCU2-Changelog.2.59.7.pdf

Restart Required: Yes

Instructions:

1. Log into the HomeMatic WebUI. 2. Navigate to Settings → System Control → Update. 3. Click 'Check for updates' and install the latest firmware. 4. Reboot the device after installation completes.

🔧 Temporary Workarounds

Network Isolation

all

Place the HomeMatic device on an isolated VLAN with no internet access and restrict inbound connections to trusted management IPs only.

WebUI Access Restriction

linux

Configure firewall rules to block all external access to the WebUI port (default TCP 80/443) and only allow access from specific trusted IP addresses.

iptables -A INPUT -p tcp --dport 80 -s TRUSTED_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

🧯 If You Can't Patch

Immediately disconnect the device from the internet and place it behind a firewall with strict inbound/outbound rules.
Disable the WebUI entirely if remote management is not required, or use VPN-only access for management.

🔍 How to Verify

Check if Vulnerable:

Check the firmware version in the WebUI under Settings → System Control → Version. If version is ≤2.57.5 (CCU2) or ≤3.57.5 (CCU3), the device is vulnerable.

Check Version:

curl -s http://CCU_IP/api/version or check via WebUI interface

Verify Fix Applied:

After updating, verify the firmware version shows 2.59.7 or higher for CCU2, or 3.59.6 or higher for CCU3.

📡 Detection & Monitoring

Log Indicators:

Unusual HTTP POST requests to WebUI endpoints
Suspicious command execution patterns in system logs
Unexpected root-level process creation

Network Indicators:

HTTP requests with unusual parameters to port 80/443 of HomeMatic devices
Outbound connections from HomeMatic devices to suspicious IPs

SIEM Query:

source="homematic" AND (http_method="POST" AND uri_path="/api/*" AND http_user_agent NOT IN ("trusted_agents"))

📊 Metadata

CVE ID: CVE-2021-33032

CVSS v3 Score: 10.0 (CRITICAL)

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

CWE: CWE-78

Published: July 22, 2021

Last Updated: November 21, 2024

🔗 References

https://novag.github.io/posts/homematic-unauthenticated-remote-code-execution/ Exploit,Third Party Advisory
https://www.eq-3.de/downloads/software/HM-CCU2-Firmware_Updates/HM-CCU-2.59.7/HM-CCU2-Changelog.2.59.7.pdf Release Notes,Vendor Advisory
https://www.eq-3.de/downloads/software/firmware/ccu3-firmware/CCU3-Changelog.3.59.6.pdf Release Notes,Vendor Advisory
https://novag.github.io/posts/homematic-unauthenticated-remote-code-execution/ Exploit,Third Party Advisory
https://www.eq-3.de/downloads/software/HM-CCU2-Firmware_Updates/HM-CCU-2.59.7/HM-CCU2-Changelog.2.59.7.pdf Release Notes,Vendor Advisory
https://www.eq-3.de/downloads/software/firmware/ccu3-firmware/CCU3-Changelog.3.59.6.pdf Release Notes,Vendor Advisory

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