Microsoft Azure Network Security Group Flow Logs are a feature of Azure Network Watcher that provide information about ingress and egress IP traffic through a configured Network Security Group. The NetWitness plugin built for Azure NSG can authenticate and pull flow logs from Azure storage in real time.
“While Virtual Network (VNET) is the cornerstone of Azure networking model and provides isolation and protection. Network Security Group (NSG) is the main tool you need to use to enforce and control network traffic rules at the networking level. Customers can control access by permitting or denying communication between the workloads within a virtual network, from systems on customer’s networks via cross-premises connectivity, or direct Internet communication. In the diagram below, both VNETs and NSGs reside in a specific layer in the Azure overall security stack, where NSGs, UDR, and network virtual appliances can be used to create security boundaries to protect the application deployments in the protected network.”
What is a Network Security Group (NSG)?
How does it work?
These flow logs are written in JSON format and show outbound and inbound flows on a per rule basis.
It provides the following information:
- MAC Address of the NIC, flow applies to
- 5-tuple information about the flow (Source IP, Destination IP, Source Port, Destination Port, Protocol),
- And if the traffic was allowed or denied.
Flow logs are stored only within a storage account and follow the logging path as shown below:
Logs have a retention policy that can be set from 1 day to 365 days. If a retention policy is not set, the logs are maintained forever. RSA Netwitness uses Shared Access Signature (SAS Token) to authenticate and pull flow logs from Azure storage in real time.
With the visibility into Network Flow traffic in the Azure framework, multiple use-cases can be built. For example:
- See the overall stats of Allowed vs Denied Traffic in your network, and based on what’s normal, setup alerts if its above or below a certain threshold.
- Summary of Protocol usage in the environment, set alerts for abnormal protocol usage.
- Top Destination Address Reached out to from your environment.
- Set Alerts against blacklisted IP Addresses
- Setup rules based on IP range to determine Inbound vs Outbound vs Lateral traffic and then build a dashboard to see the pattern.
Downloads and Documentation:
Configuration Guide: Microsoft Azure NSG Event Source Configuration Guide
Collector Package on RSA Live: "MS Azure NSG Flow Logs"
Parser on RSA Live: CEF (device.type="msazurensg")
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