This ALERT contains mitigations for the active exploitation of vulnerabilities in Microsoft Exchange on-premises products.
1. EXECUTIVE SUMMARY
CISA is aware of reports detailing active exploitation of vulnerabilities in Microsoft Exchange on-premises products. These products are often found on industrial control system networks, and an exploitation may allow an attacker entry into the network. DHS has published Emergency Directive 21-02 for this issue, and the main purpose of this alert is to call attention to this document.
Emergency Directive 21-02 requires all U.S. federal government agencies to immediately apply patches to applicable Microsoft Exchange products.
CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures. Apply Microsoft patches for Microsoft Exchange servers as soon as possible.
CISA recommends, as quality assurance, users test the update in a test development environment that reflects their production environment prior to installation. In addition, users should:
- Minimize network exposure for all control system devices and/or systems and ensure that they are not accessible from the Internet.
- Locate control system networks and remote devices behind Policy Enforcement Points (firewalls) and isolate them from the business network.
- When remote access is required, use secure methods, such as virtual private networks (VPNs), recognizing VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize a VPN is only as secure as the connected devices.
CISA also provides a section for control systems security recommended practices on the ICS webpage on us-cert.cisa.gov. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.
Additional mitigation guidance and recommended practices are publicly available on the ICS webpage on us-cert.cisa.gov in the Technical Information Paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies.