CVE-2021-31883 – This vulnerability affects Siemens Capital Embe... (How to Fix)

Q: What is the severity of CVE-2021-31883?

CVE-2021-31883 has a CVSS score of 7.1 (HIGH). This vulnerability affects Siemens Capital Embedded AR Classic products where the DHCP client fails to validate vendor option lengths in DHCP ACK messages. Attackers can send specially crafted DHCP packets to cause denial-of-service conditions. Affected systems include Capital Embedded AR Classic 431-422 and R20-11 versions.

📋 TL;DR

This vulnerability affects Siemens Capital Embedded AR Classic products where the DHCP client fails to validate vendor option lengths in DHCP ACK messages. Attackers can send specially crafted DHCP packets to cause denial-of-service conditions. Affected systems include Capital Embedded AR Classic 431-422 and R20-11 versions.

💻 Affected Systems

Products:

Siemens Capital Embedded AR Classic 431-422
Siemens Capital Embedded AR Classic R20-11

Versions: All versions of 431-422; R20-11 versions before V2303

Operating Systems: Embedded systems running Siemens Capital software

Default Config Vulnerable: ⚠️ Yes

Notes: Requires DHCP client functionality to be enabled and processing DHCP ACK messages.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system crash or unavailability of affected embedded systems, potentially disrupting industrial operations.

🟠

Likely Case

Temporary service disruption or system reboot when malicious DHCP packets are received.

🟢

If Mitigated

Minimal impact with proper network segmentation and DHCP server controls.

🌐 Internet-Facing: LOW - Industrial control systems typically shouldn't be directly internet-facing.

🏢 Internal Only: MEDIUM - Attackers on the local network could exploit this to disrupt operations.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires network access to send malicious DHCP packets to vulnerable systems.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: V2303 for R20-11 series

Vendor Advisory: https://cert-portal.siemens.com/productcert/html/ssa-044112.html

Restart Required: Yes

Instructions:

1. Download update V2303 from Siemens support portal. 2. Apply update to affected R20-11 systems. 3. For 431-422 systems, contact Siemens for specific guidance as all versions are affected. 4. Restart systems after patching.

🔧 Temporary Workarounds

Network Segmentation

all

Isolate affected systems from untrusted networks and restrict DHCP traffic.

DHCP Server Hardening

all

Configure trusted DHCP servers only and implement DHCP snooping on network switches.

🧯 If You Can't Patch

Implement strict network segmentation to isolate vulnerable systems
Deploy network monitoring for anomalous DHCP traffic patterns

🔍 How to Verify

Check if Vulnerable:

Check system version against affected versions: 431-422 (all versions) or R20-11 (versions < V2303)

Check Version:

System-specific Siemens Capital software version check (consult product documentation)

Verify Fix Applied:

Verify system version is V2303 or higher for R20-11 series

📡 Detection & Monitoring

Log Indicators:

System crash logs
DHCP client error messages
Unexpected system reboots

Network Indicators:

Malformed DHCP packets with oversized vendor options
DHCP traffic from unauthorized sources

SIEM Query:

DHCP packets with option_length > normal_threshold OR source_ip not in trusted_dhcp_servers

📊 Metadata

CVE ID: CVE-2021-31883

CVSS v3 Score: 7.1 (HIGH)

CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

CWE: CWE-119

Published: November 9, 2021

Last Updated: November 21, 2024

🔗 References

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

If you're affected by CVE-2021-31883, you might also want to check these: