CVE-2023-41101 – This vulnerability in OpenNDS captive portal al... (How to Fix)

Q: What is the severity of CVE-2023-41101?

CVE-2023-41101 has a CVSS score of 9.8 (CRITICAL). This vulnerability in OpenNDS captive portal allows attackers to trigger buffer overflows via specially crafted GET requests. It affects OpenNDS versions before 10.1.3 and can lead to denial-of-service or remote code execution. Organizations using OpenNDS for network access control are at risk.

📋 TL;DR

This vulnerability in OpenNDS captive portal allows attackers to trigger buffer overflows via specially crafted GET requests. It affects OpenNDS versions before 10.1.3 and can lead to denial-of-service or remote code execution. Organizations using OpenNDS for network access control are at risk.

💻 Affected Systems

Products:

OpenNDS

Versions: All versions before 10.1.3

Operating Systems: Linux-based systems running OpenNDS

Default Config Vulnerable: ⚠️ Yes

Notes: Affects both stack-based buffer overflow in versions 9.x and earlier, and heap-based buffer overflow in versions 10.x and later.

📦 What is this software?

Opennds by Opennds

View all CVEs affecting Opennds →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with full system compromise, allowing attackers to execute arbitrary commands on the OpenNDS server.

🟠

Likely Case

Denial-of-service causing captive portal to crash, disrupting network access for users.

🟢

If Mitigated

Limited impact if proper network segmentation and access controls prevent external exploitation.

🌐 Internet-Facing: HIGH - Captive portals are typically internet-facing and accessible to unauthenticated users.

🏢 Internal Only: MEDIUM - Internal users could still exploit if they have network access to the portal.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending specially crafted GET requests to the captive portal endpoint.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 10.1.3 or later (10.2.0 recommended)

Vendor Advisory: https://github.com/openNDS/openNDS/releases/tag/v10.1.3

Restart Required: Yes

Instructions:

1. Backup current configuration. 2. Update OpenNDS to version 10.1.3 or later. 3. Restart OpenNDS service. 4. Verify the service is running correctly.

🔧 Temporary Workarounds

Network Access Restriction

linux

Restrict access to OpenNDS captive portal to trusted networks only

iptables -A INPUT -p tcp --dport 2050 -s TRUSTED_NETWORK -j ACCEPT
iptables -A INPUT -p tcp --dport 2050 -j DROP

🧯 If You Can't Patch

Implement network segmentation to isolate OpenNDS from untrusted networks
Deploy WAF or reverse proxy with request size limits and input validation

🔍 How to Verify

Check if Vulnerable:

Check OpenNDS version: opennds --version or ps aux | grep opennds

Check Version:

opennds --version

Verify Fix Applied:

Confirm version is 10.1.3 or higher and test captive portal functionality

📡 Detection & Monitoring

Log Indicators:

Unusually long query strings in HTTP GET requests
OpenNDS service crashes or restarts
Memory violation errors in system logs

Network Indicators:

HTTP GET requests with excessively long query parameters to port 2050
Multiple connection attempts with varying query string lengths

SIEM Query:

source="opennds.log" AND ("GET" AND uri_query.length>1024) OR "segmentation fault" OR "buffer overflow"

📊 Metadata

CVE ID: CVE-2023-41101

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-787

Published: November 17, 2023

Last Updated: November 21, 2024

🔗 References

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