CVE-2021-33536

Q: What is the severity of CVE-2021-33536?

CVE-2021-33536 has a CVSS score of 7.5 (HIGH). This vulnerability allows unauthenticated attackers to send specially crafted packets to Weidmueller Industrial WLAN devices, causing an integer underflow that triggers a denial-of-service condition. The exploit can crash the device by accessing unmapped or out-of-bounds memory. Industrial organizations using affected Weidmueller WLAN equipment are at risk.

7.5 HIGH

Denial of Service

📋 TL;DR

This vulnerability allows unauthenticated attackers to send specially crafted packets to Weidmueller Industrial WLAN devices, causing an integer underflow that triggers a denial-of-service condition. The exploit can crash the device by accessing unmapped or out-of-bounds memory. Industrial organizations using affected Weidmueller WLAN equipment are at risk.

💻 Affected Systems

Products:

Weidmueller Industrial WLAN devices

Versions: Multiple versions (specific versions not detailed in provided references)

Operating Systems: Embedded firmware

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations appear vulnerable. The vulnerability exists in the ServiceAgent functionality.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete device crash requiring physical reset or replacement, disrupting industrial network connectivity and potentially affecting operational processes.

🟠

Likely Case

Service disruption on affected WLAN devices requiring manual intervention to restore functionality.

🟢

If Mitigated

Limited impact if devices are behind firewalls with proper network segmentation and packet filtering.

🌐 Internet-Facing: HIGH - Unauthenticated remote exploitation makes internet-facing devices particularly vulnerable.

🏢 Internal Only: MEDIUM - Internal attackers or malware could still exploit this vulnerability to disrupt industrial networks.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW - Unauthenticated exploitation with specially crafted packets.

The vulnerability is triggered by sending a specially crafted packet to the ServiceAgent functionality.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Not specified in provided references

Vendor Advisory: https://cert.vde.com/en-us/advisories/vde-2021-026

Restart Required: Yes

Instructions:

1. Contact Weidmueller support for firmware updates. 2. Download latest firmware from vendor portal. 3. Apply firmware update following vendor instructions. 4. Reboot device after update.

🔧 Temporary Workarounds

Network Segmentation

all

Isolate Weidmueller WLAN devices in separate network segments with strict firewall rules.

Access Control Lists

all

Implement ACLs to restrict access to ServiceAgent ports from trusted sources only.

🧯 If You Can't Patch

Implement strict network segmentation to isolate affected devices
Deploy intrusion prevention systems to detect and block exploit attempts

🔍 How to Verify

Check if Vulnerable:

Check device firmware version against vendor advisory. Monitor for unexpected device crashes or service disruptions.

Check Version:

Check via device web interface or CLI (vendor-specific commands)

Verify Fix Applied:

Verify firmware version has been updated to patched version. Test device stability under normal operation.

📡 Detection & Monitoring

Log Indicators:

Unexpected device reboots
ServiceAgent process crashes
Memory access violation logs

Network Indicators:

Unusual packets to ServiceAgent ports
Traffic patterns matching exploit attempts

SIEM Query:

source="weidmueller_wlan" AND (event_type="crash" OR event_type="memory_violation")

📊 Metadata

CVE ID: CVE-2021-33536

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-191

Published: June 25, 2021

Last Updated: November 21, 2024

🔗 References

https://cert.vde.com/en-us/advisories/vde-2021-026 Third Party Advisory
https://cert.vde.com/en-us/advisories/vde-2021-026 Third Party Advisory