​
Event Information

  • The UpdateSizeConstraintSet event in AWS WAF refers to a change made to a size constraint set, which is a collection of rules that specify the maximum allowed size for specific parts of web requests.
  • This event indicates that a modification has been made to the configuration of the size constraint set, such as adding or removing rules, changing the maximum size limits, or updating the conditions for applying the constraints.
  • It is important to monitor and analyze this event to ensure that the size constraint set is properly configured to protect against potential attacks that exploit oversized requests.

​
Examples

  • If the UpdateSizeConstraintSet operation is not properly configured, it can potentially impact security by allowing malicious requests to bypass size constraints. For example:
    1. If the size constraint is set too high or not properly defined, it may allow large requests to consume excessive resources, leading to denial of service attacks.
    2. If the size constraint is set too low, legitimate requests may be blocked or rejected, impacting the availability of the application.
    3. If the size constraint is not properly applied to all relevant parts of the request (e.g., headers, body), it may allow attackers to bypass the constraint and send malicious payloads.

​
Remediation

​
Using Console

  1. Identify the specific AWS WAF rule that needs to be remediated based on the examples provided.

    • Log in to the AWS Management Console.
    • Navigate to the AWS WAF service.
    • Select the appropriate WebACL that contains the rule that needs to be remediated.

  2. Modify the AWS WAF rule to address the identified issue.

    • Within the selected WebACL, locate the rule that needs to be remediated.
    • Click on the rule to access its configuration settings.
    • Adjust the rule’s conditions, filters, or actions as necessary to address the issue.
    • Save the changes made to the rule.

  3. Test and monitor the remediated AWS WAF rule.

    • Deploy the updated WebACL to the appropriate AWS resources (e.g., CloudFront distribution, Application Load Balancer).
    • Monitor the traffic and logs to ensure that the remediated rule is functioning as expected.
    • Continuously monitor and analyze the logs and metrics to identify any potential issues or anomalies.
    • Make further adjustments to the rule if necessary based on the observed behavior.

​
Using CLI

  1. To remediate a specific rule in AWS WAF using AWS CLI, you can use the update-rule command. For example, if you want to update a rule with the ID 12345678-1234-1234-1234-123456789012 in a WebACL named MyWebACL, you can use the following command:

    aws wafv2 update-rule --name MyWebACL --scope REGIONAL --id 12345678-1234-1234-1234-123456789012 --action ALLOW --override-action NONE

    This command updates the specified rule in the WebACL, setting the action to ALLOW and overriding any previous actions.

  2. To remediate a rate-based rule in AWS WAF using AWS CLI, you can use the update-rate-based-rule command. For example, if you want to update a rate-based rule with the ID 12345678-1234-1234-1234-123456789012 in a WebACL named MyWebACL, you can use the following command:

    aws wafv2 update-rate-based-rule --name MyWebACL --scope REGIONAL --id 12345678-1234-1234-1234-123456789012 --rate-limit 1000

    This command updates the specified rate-based rule in the WebACL, setting the rate limit to 1000 requests per 5 minutes.

  3. To remediate a managed rule group in AWS WAF using AWS CLI, you can use the update-managed-rule-set-version command. For example, if you want to update a managed rule group with the ARN arn:aws:wafv2:us-west-2:123456789012:managed-rule-set/aws-managed/gbqj2j5k5k to the latest available version, you can use the following command:

    aws wafv2 update-managed-rule-set-version --name gbqj2j5k5k --scope REGIONAL --vendor-name aws-managed --managed-rule-set-id arn:aws:wafv2:us-west-2:123456789012:managed-rule-set/aws-managed/gbqj2j5k5k

    This command updates the specified managed rule group to the latest available version, ensuring that you have the latest rule definitions and protections in place.

​
Using Python

  1. Example 1: Blocking IP addresses with AWS WAF using Python
    • Use the AWS SDK for Python (Boto3) to interact with AWS WAF.
    • Write a Python script to retrieve the IP addresses that need to be blocked.
    • Use the create_ip_set method to create an IP set in AWS WAF.
    • Use the update_ip_set method to add the retrieved IP addresses to the IP set.
    • Use the update_web_acl method to associate the IP set with the desired web ACL.
import boto3

# Create AWS WAF client
waf_client = boto3.client('waf')

# Retrieve IP addresses to block
ip_addresses = ['192.0.2.1', '203.0.113.2']

# Create IP set
response = waf_client.create_ip_set(
    Name='BlockedIPSet',
    ChangeToken='CHANGE_TOKEN'
)

# Add IP addresses to IP set
response = waf_client.update_ip_set(
    IPSetId='IP_SET_ID',
    ChangeToken='CHANGE_TOKEN',
    Updates=[
        {
            'Action': 'INSERT',
            'IPSetDescriptor': {
                'Type': 'IPV4',
                'Value': ip_address
            }
        }
        for ip_address in ip_addresses
    ]
)

# Associate IP set with web ACL
response = waf_client.update_web_acl(
    WebACLId='WEB_ACL_ID',
    ChangeToken='CHANGE_TOKEN',
    Updates=[
        {
            'Action': 'INSERT',
            'ActivatedRule': {
                'Priority': 1,
                'RuleId': 'BLOCK_RULE_ID',
                'Action': {
                    'Type': 'BLOCK'
                }
            }
        }
    ]
)
  1. Example 2: Creating rate-based rules with AWS WAF using Python
    • Use the AWS SDK for Python (Boto3) to interact with AWS WAF.
    • Write a Python script to define the rate-based rule parameters.
    • Use the create_rate_based_rule method to create a rate-based rule in AWS WAF.
    • Use the update_web_acl method to associate the rate-based rule with the desired web ACL.
import boto3

# Create AWS WAF client
waf_client = boto3.client('waf')

# Define rate-based rule parameters
rule_name = 'RateBasedRule'
metric_name = 'RequestCount'
rate_limit = 100
rate_key = 'IP'

# Create rate-based rule
response = waf_client.create_rate_based_rule(
    Name=rule_name,
    MetricName=metric_name,
    RateLimit=rate_limit,
    ChangeToken='CHANGE_TOKEN'
)

# Associate rate-based rule with web ACL
response = waf_client.update_web_acl(
    WebACLId='WEB_ACL_ID',
    ChangeToken='CHANGE_TOKEN',
    Updates=[
        {
            'Action': 'INSERT',
            'ActivatedRule': {
                'Priority': 1,
                'RuleId': 'RATE_BASED_RULE_ID',
                'Action': {
                    'Type': 'BLOCK'
                }
            }
        }
    ]
)
  1. Example 3: Creating custom rules with AWS WAF using Python
    • Use the AWS SDK for Python (Boto3) to interact with AWS WAF.
    • Write a Python script to define the custom rule parameters.
    • Use the create_rule method to create a custom rule in AWS WAF.
    • Use the update_web_acl method to associate the custom rule with the desired web ACL.
import boto3

# Create AWS WAF client
waf_client = boto3.client('waf')

# Define custom rule parameters
rule_name = 'CustomRule'
predicate_type = 'IPMatch'
predicate_value = '192.0.2.1'

# Create custom rule
response = waf_client.create_rule(
    Name=rule_name,
    MetricName='CustomRule',
    ChangeToken='CHANGE_TOKEN',
    Predicates=[
        {
            'DataId': 'IP_MATCH_DATA_ID',
            'Negated': False,
            'Type': predicate_type,
            'Value': predicate_value
        }
    ]
)

# Associate custom rule with web ACL
response = waf_client.update_web_acl(
    WebACLId='WEB_ACL_ID',
    ChangeToken='CHANGE_TOKEN',
    Updates=[
        {
            'Action': 'INSERT',
            'ActivatedRule': {
                'Priority': 1,
                'RuleId': 'CUSTOM_RULE_ID',
                'Action': {
                    'Type': 'BLOCK'
                }
            }
        }
    ]
)