CVE-2021-34581 – This CVE describes a memory leak vulnerability ... (How to Fix)

Q: What is the severity of CVE-2021-34581?

CVE-2021-34581 has a CVSS score of 7.5 (HIGH). This CVE describes a memory leak vulnerability in OpenSSL implementation on specific WAGO PLC devices. Unauthenticated attackers can cause denial-of-service by exhausting device memory, affecting WAGO 750 series devices running firmware versions FW4 through FW15.

📋 TL;DR

This CVE describes a memory leak vulnerability in OpenSSL implementation on specific WAGO PLC devices. Unauthenticated attackers can cause denial-of-service by exhausting device memory, affecting WAGO 750 series devices running firmware versions FW4 through FW15.

💻 Affected Systems

Products:

WAGO 750-831
WAGO 750-880
WAGO 750-881
WAGO 750-889

Versions: FW4 up to FW15

Operating Systems: Embedded Linux-based firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Affects OpenSSL implementation in WAGO's firmware; specific configurations may vary by device model.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete device unavailability requiring physical reset or power cycle, potentially disrupting industrial processes.

🟠

Likely Case

Device becomes unresponsive or crashes, requiring manual intervention to restore functionality.

🟢

If Mitigated

Minimal impact with proper network segmentation and monitoring to detect exploitation attempts.

🌐 Internet-Facing: HIGH - Unauthenticated remote exploitation allows attackers to directly target exposed devices.

🏢 Internal Only: MEDIUM - Internal attackers or malware could still exploit, but requires network access.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW - Simple memory exhaustion attack possible without authentication.

Exploitation requires network access to the device's OpenSSL services.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: FW16 or later

Vendor Advisory: https://cert.vde.com/en-us/advisories/vde-2021-038

Restart Required: Yes

Instructions:

1. Download latest firmware from WAGO support portal. 2. Backup device configuration. 3. Apply firmware update via WAGO Service Interface or web interface. 4. Verify successful update and restore configuration if needed.

🔧 Temporary Workarounds

Network Segmentation

all

Isolate affected devices in separate network segments with strict firewall rules.

Access Control Lists

all

Implement ACLs to restrict network access to only authorized systems.

🧯 If You Can't Patch

Implement strict network segmentation and firewall rules to limit access
Monitor device memory usage and restart devices if abnormal patterns detected

🔍 How to Verify

Check if Vulnerable:

Check firmware version via web interface or WAGO Service Interface; versions FW4-FW15 are vulnerable.

Check Version:

Check via web interface at http://<device-ip>/version or using WAGO Service Tools

Verify Fix Applied:

Confirm firmware version is FW16 or later and monitor for memory leak symptoms.

📡 Detection & Monitoring

Log Indicators:

Memory exhaustion warnings
Device crash/restart logs
High memory usage alerts

Network Indicators:

Unusual traffic patterns to device OpenSSL ports
Multiple connection attempts from single sources

SIEM Query:

source="wago_device" AND (message="memory" OR message="crash" OR message="restart")

📊 Metadata

CVE ID: CVE-2021-34581

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-772

Published: August 31, 2021

Last Updated: November 21, 2024

🔗 References

https://cert.vde.com/en-us/advisories/vde-2021-038 Third Party Advisory
https://cert.vde.com/en-us/advisories/vde-2021-038 Third Party Advisory

📤 Share & Export

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