CVE-2021-25659
📋 TL;DR
A denial-of-service vulnerability in Siemens Automation License Manager allows attackers to crash the service by sending specially crafted packets to TCP port 4410. This affects all versions of Automation License Manager 5 and versions of Automation License Manager 6 before V6.0 SP9 Update 2, preventing legitimate users from accessing license management functionality.
💻 Affected Systems
- Siemens Automation License Manager 5
- Siemens Automation License Manager 6
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete service outage of Automation License Manager, disrupting industrial automation systems that depend on license validation, potentially halting production processes.
Likely Case
Temporary denial-of-service affecting license management operations until service restart, causing operational delays in industrial environments.
If Mitigated
Minimal impact with proper network segmentation and monitoring, allowing quick detection and response to attack attempts.
🎯 Exploit Status
Exploitation requires sending crafted packets to port 4410, which is relatively simple but specific packet structure details are not publicly documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Automation License Manager 6 V6.0 SP9 Update 2
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-158827.pdf
Restart Required: Yes
Instructions:
1. Download ALM 6 V6.0 SP9 Update 2 from Siemens support portal. 2. Stop ALM service. 3. Install update. 4. Restart service. For ALM 5, migrate to ALM 6 and apply patch.
🔧 Temporary Workarounds
Network Access Control
allRestrict access to port 4410/tcp using firewall rules to only trusted hosts/networks.
Windows Firewall: New-NetFirewallRule -DisplayName "Block ALM 4410" -Direction Inbound -LocalPort 4410 -Protocol TCP -Action Block
Linux iptables: iptables -A INPUT -p tcp --dport 4410 -j DROP
Service Port Change
windowsChange the default port from 4410 to a non-standard port if supported by your configuration.
Modify ALM configuration file to change listening port (consult Siemens documentation for specific file location)
🧯 If You Can't Patch
- Implement strict network segmentation to isolate ALM systems from untrusted networks.
- Deploy network intrusion detection systems to monitor for anomalous traffic patterns on port 4410.
🔍 How to Verify
Check if Vulnerable:
Check ALM version via Control Panel > Programs and Features (Windows) or using Siemens diagnostic tools. If ALM 5 any version or ALM 6 version < V6.0 SP9 Update 2, system is vulnerable.Check Version:
Windows: wmic product where "name like 'Automation License Manager%'" get versionVerify Fix Applied:
Verify installed version is ALM 6 V6.0 SP9 Update 2 or later. Test service functionality and monitor for crashes after applying patch.📡 Detection & Monitoring
Log Indicators:
- Service crash events in Windows Event Log (Application/Security)
- High memory consumption alerts from ALM process
Network Indicators:
- Unusual traffic volume to port 4410/tcp
- Multiple connection attempts from single source to port 4410
SIEM Query:
source="windows" event_id=1000 process_name="almsrv.exe" OR destination_port=4410 AND bytes_sent>10000