CVE-2024-46556 – A buffer overflow vulnerability in Draytek Vigo... (How to Fix)

📋 TL;DR

A buffer overflow vulnerability in Draytek Vigor 3910 routers allows attackers to cause Denial of Service (DoS) by sending crafted input to the sInRCSecret0 parameter. This affects organizations using Draytek Vigor 3910 routers with vulnerable firmware. The vulnerability is remotely exploitable without authentication.

💻 Affected Systems

Products:

Draytek Vigor 3910

Versions: v4.3.2.6 (specific version mentioned in CVE)

Operating Systems: Draytek proprietary firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects the specific firmware version mentioned; other versions may also be vulnerable but not confirmed

📦 What is this software?

Vigor3910 Firmware by Draytek

View all CVEs affecting Vigor3910 Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete router crash requiring physical reboot, potential for remote code execution if buffer overflow can be controlled precisely

🟠

Likely Case

Router becomes unresponsive, requiring reboot and causing network downtime

🟢

If Mitigated

Limited to DoS impact with quick recovery if monitoring and backup systems are in place

🌐 Internet-Facing: HIGH - The vulnerability is in an internet-facing CGI endpoint and requires no authentication

🏢 Internal Only: MEDIUM - Internal attackers could still exploit, but external threat is more significant

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW - Simple buffer overflow via HTTP request

The vulnerability is in a CGI endpoint accessible via HTTP, making exploitation straightforward

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Unknown

Vendor Advisory: Not available

Restart Required: Yes

Instructions:

1. Check Draytek website for firmware updates
2. Download latest firmware for Vigor 3910
3. Upload firmware via web interface
4. Reboot router after update

🔧 Temporary Workarounds

Block access to v2x00.cgi

linux

Use firewall rules to block external access to the vulnerable CGI endpoint

iptables -A INPUT -p tcp --dport 80 -m string --string "v2x00.cgi" --algo bm -j DROP

Disable unused services

all

Disable any unnecessary services on the router to reduce attack surface

🧯 If You Can't Patch

Segment network to isolate Vigor 3910 from critical systems
Implement strict firewall rules to limit access to router management interface

🔍 How to Verify

Check if Vulnerable:

Check firmware version in router web interface under System Maintenance > Firmware Information

Check Version:

curl -s http://router-ip/cgi-bin/version.cgi | grep Firmware

Verify Fix Applied:

Verify firmware version is newer than v4.3.2.6 after update

📡 Detection & Monitoring

Log Indicators:

Multiple requests to v2x00.cgi with long parameters
Router reboot events in system logs
HTTP 500 errors from CGI endpoints

Network Indicators:

Unusual HTTP POST requests to /cgi-bin/v2x00.cgi
Router becoming unresponsive to ping

SIEM Query:

source="router_logs" AND (uri="*/v2x00.cgi*" OR message="*buffer overflow*" OR message="*segmentation fault*")

📊 Metadata

CVE ID: CVE-2024-46556

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

CWE: CWE-120

Published: September 18, 2024

Last Updated: March 18, 2025

🔗 References

https://ink-desk-28f.notion.site/Draytek-vigor-3910-Analysis-Report-b3b23e150c4f4bab822c3c47fd7b9de9#a26d36d8c8d042299348d8ec7a0260ca Permissions Required

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