---
title: Inbound UDP NetBIOS access should be restricted
description: Datadog, the leading service for cloud-scale monitoring.
breadcrumbs: >-
  Docs > Datadog Security > OOTB Rules > Inbound UDP NetBIOS access should be
  restricted
---

# Inbound UDP NetBIOS access should be restricted
 
## Description{% #description %}

Reduce the probability of a breach by checking [EC2 security groups](https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html) for inbound rules that allow unfettered access to TCP port 139 and UDP ports 137 and 138 (used by services for NetBIOS name resolution) and restrict access to IP addresses that require this port.

## Rationale{% #rationale %}

Malicious activity, such as bad tunnel exploits or denial-of-service (DoS) and man-in-the-middle (MITM) attacks, can occur when permitting unfettered access to this port.

## Remediation{% #remediation %}

### From the console{% #from-the-console %}

Follow the [Security group rules](https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html#SecurityGroupRules) docs to learn how to add a security group rule that will restrict access to a specific port.

### From the command line{% #from-the-command-line %}

1. Run `authorize-security-group-ingress` to [add new inbound rules](https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/authorize-security-group-ingress.html) that restrict UDP ports 137 access.

In the `revoke-security-group-ingress.sh` file:

   ```bash
       aws ec2 authorize-security-group-ingress
           --group-name your-group-name
           --protocol udp
           --port 137
           --cidr 192.0.2.0/24
       
```

1. Run `authorize-security-group-ingress` to [add new inbound rules](https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/authorize-security-group-ingress.html) that restrict UDP ports 138 access.

In the `revoke-security-group-ingress.sh` file:

   ```bash
       aws ec2 authorize-security-group-ingress
           --group-name your-group-name
           --protocol udp
           --port 138
           --cidr 192.0.2.0/24
       
```