Blocking Instant Messaging Services on Cisco ASA Post-9.7: A Modern Approach

Blocking Instant Messaging Services on Cisco ASA Post-9.7

With the rise of Instant Messaging (IM) applications such as Microsoft MSN and Yahoo IM, managing the security risks associated with their various services (chat, conferencing, file transfer, webcam, etc.) is crucial. These services can expose your network to potential vulnerabilities, such as malicious file uploads or unauthorized access to sensitive data.

Before Cisco ASA 9.7, blocking IM required complex Modular Policy Framework (MPF) and Layer-7 configurations. Post-9.7, FirePOWER NGFW capabilities dramatically simplify this process.

📉 Why the Old Approach Was Challenging ➕

• Multiple L7 class-maps and policy-maps were required
• Each IM feature needed separate inspection logic
• User-specific blocks required additional handling
• High operational complexity and maintenance overhead

Legacy MPF-based IM blocking was powerful but fragile and difficult to scale.

🚀 Modern Approach: FirePOWER Post-9.7 ➕

FirePOWER introduces Application Visibility and Control (AVC), allowing IM traffic to be identified and controlled at the application and sub-application level.

INTERNAL USER | v [ ASA DATA PLANE ] | v [ FirePOWER AVC Engine ] | +--> Application: MSN / Yahoo IM | +--> Chat → ALLOW +--> File Tx → BLOCK +--> Webcam → BLOCK +--> Conference → BLOCK

FirePOWER understands IM behavior natively—no protocol decoding required.

🔒 Blocking Specific IM Services ➕

Using FirePOWER Application Filtering, you can selectively block high-risk IM services while permitting basic chat functionality.

• Create or modify an Access Control Policy
• Set Source Zone: Inside
• Set Destination Zone: Outside
• Select MSN and Yahoo IM applications
• Block File Transfer, Webcam, Conference, Games
• Deploy the policy

RULE #10 (GENERAL USERS) ---------------------------------- Source: Inside Destination: Internet Application: MSN / Yahoo IM Action: - Chat → ALLOW - File Tx → BLOCK - Webcam → BLOCK

🚫 Blocking a Specific User Completely ➕

FirePOWER allows IP-based and application-based logic to be combined seamlessly.

• Create a higher-priority Access Control Rule
• Match the specific user’s IP address
• Block all IM applications
• Place the rule above the general IM rule

RULE #1 (SPECIFIC USER) ---------------------------------- Source IP: 192.168.10.25 Application: ALL IM Action: BLOCK ⬇ (Rule Order) RULE #10 (ALL USERS) ---------------------------------- IM with limited features

Rule order is critical. User-specific deny rules must be evaluated first.

📊 Monitoring & Reporting ➕

• View blocked IM traffic under Analysis → Connections → Events
• Filter by application (MSN, Yahoo IM)
• Monitor bypass attempts via Intrusion → Events
• Set alerts for repeated violations

FirePOWER provides forensic-level visibility unavailable with legacy ASA inspection.

✅ Key Takeaways

• FirePOWER replaces complex MPF L7 inspection
• Granular IM service control is native and scalable
• User-specific and application-specific logic coexist cleanly
• Rule order determines enforcement accuracy
• Post-9.7 ASA offers visibility, not just blocking

Cisco ASA Post-9.7 • FirePOWER NGFW • IM Control Done Right