Network-Acl — CraftedSignal Threat Feed

AWS Network ACL Deletion Detected

hello@craftedsignal.io — Wed, 03 Jan 2024 12:00:00 +0000

This analytic identifies the deletion of AWS Network Access Control Lists (ACLs), a critical security control, using AWS CloudTrail logs. The detection focuses on DeleteNetworkAclEntry events, triggered when a user removes a network ACL entry. This is significant because deleting a network ACL can inadvertently or maliciously remove critical access restrictions, potentially opening cloud instances to unauthorized access. The targeted action allows attackers to bypass network security controls, potentially leading to data exfiltration or further compromise of the cloud environment. The detection leverages logs from AWS CloudTrail and requires the AWS App for Splunk (version 5.1.0 or later) and Splunk Add-on for AWS (version 4.4.0 or later).

Attack Chain

An attacker gains initial access to an AWS account, possibly through compromised credentials or exploiting a vulnerability in an application running on EC2.
The attacker enumerates existing Network ACLs to identify potential targets for modification or deletion.
The attacker identifies a Network ACL that, when removed or modified, would grant them broader access to resources within the VPC.
The attacker uses AWS CLI or AWS Management Console to issue a DeleteNetworkAclEntry command, targeting the chosen ACL.
AWS CloudTrail logs the DeleteNetworkAclEntry event, capturing details such as the user identity, timestamp, and affected ACL.
The targeted Network ACL entry is removed, altering the network access rules for the associated subnets.
The attacker leverages the new network access to connect to previously restricted resources, such as databases or internal applications.
The attacker exfiltrates sensitive data or performs other malicious activities, bypassing network-level security controls.

Impact

Successful deletion of a network ACL entry can lead to unauthorized access to critical AWS resources, potentially affecting all instances within the affected subnets. The impact can range from data breaches and service disruption to full compromise of the cloud environment, and depends on the scope and importance of the now-exposed resources. This poses a significant threat to organizations utilizing AWS, potentially impacting confidentiality, integrity, and availability.

Recommendation

Deploy the Sigma rule AWS Network ACL Entry Deletion to detect instances of ACL entry deletion based on DeleteNetworkAclEntry events in AWS CloudTrail.
Investigate any detected instances of DeleteNetworkAclEntry events, paying close attention to the user identity (user), source IP (src), and the specific ACL being modified.
Enable and review CloudTrail logs regularly to ensure proper coverage of AWS API activity, as indicated in the data_source section.
Implement multi-factor authentication (MFA) for all AWS accounts to mitigate the risk of compromised credentials leading to unauthorized ACL modifications.
Implement the aws_network_access_control_list_deleted_filter macro to reduce false positives.

AWS Network ACL Created with All Ports Open

hello@craftedsignal.io — Wed, 03 Jan 2024 10:00:00 +0000

This detection focuses on identifying misconfigured AWS Network ACLs (NACLs) that permit unrestricted traffic. AWS NACLs act as a firewall for controlling traffic in and out of subnets within a Virtual Private Cloud (VPC). When an NACL is configured to allow all ports and protocols from any IP address (0.0.0.0/0), it effectively bypasses security controls and exposes resources to potential threats. The activity is detected by monitoring AWS CloudTrail events for CreateNetworkAclEntry or ReplaceNetworkAclEntry API calls. This configuration error can be introduced by administrators during initial setup or through misconfiguration during updates. Defenders should ensure that NACLs follow the principle of least privilege to limit the attack surface.

Attack Chain

An attacker identifies a target AWS environment.
The attacker scans for publicly accessible services or resources.
An administrator, either maliciously or accidentally, creates or modifies a Network ACL using the AWS Management Console, CLI, or API with overly permissive rules (allowing all traffic: ruleAction=allow AND egress=false AND aclProtocol=-1 AND cidrBlock=0.0.0.0/0).
The misconfigured NACL is applied to one or more subnets within the VPC.
The attacker exploits the open ports and protocols to gain unauthorized access.
The attacker attempts to move laterally within the AWS environment.
The attacker exfiltrates sensitive data or disrupts services.

Impact

A misconfigured Network ACL that allows all traffic can have severe consequences. It can lead to unauthorized access to sensitive data, potential data breaches, service disruption, and further compromise of the AWS environment. The impact is particularly high if critical resources are located within the affected subnets. This type of misconfiguration violates security best practices and compliance requirements.

Recommendation

Deploy the Sigma rule AWS Network ACL Created with All Ports Open to your SIEM to detect this specific misconfiguration (logsource: ASL AWS CloudTrail, category: network_connection).
Review existing Network ACL configurations to identify and remediate any overly permissive rules (check AWS console or use AWS CLI/API).
Implement automated checks to validate Network ACL configurations against security best practices.
Ensure that NACLs follow the principle of least privilege by only allowing necessary traffic (review NACL ruleAction, egress, aclProtocol, and cidrBlock settings in CloudTrail logs).
Investigate any identified instances of overly permissive NACL configurations to determine the root cause and potential impact (analyze CloudTrail logs for CreateNetworkAclEntry or ReplaceNetworkAclEntry events).

AWS Network Access Control List Created with All Open Ports

hello@craftedsignal.io — Tue, 02 Jan 2024 12:00:00 +0000

This detection identifies the creation of overly permissive Network Access Control Lists (ACLs) within Amazon Web Services (AWS). Specifically, it focuses on CreateNetworkAclEntry or ReplaceNetworkAclEntry CloudTrail events where rules are configured to allow all traffic (all ports open) to a defined CIDR block. Such configurations drastically reduce network security posture by potentially exposing critical services and data to unauthorized access. The timeframe of concern is ongoing as long as such misconfigurations exist. This matters to defenders because an attacker could leverage such an opening to pivot deeper into the AWS environment, leading to data exfiltration or service disruption.

Attack Chain

An attacker gains initial access to an AWS account through compromised credentials or other means (e.g., exposed API keys).
The attacker uses the AWS CLI or Management Console to create a new Network ACL or modify an existing one.
The attacker configures the ACL rule to allow all inbound traffic (0.0.0.0/0 for all IPv4 addresses) on all ports by setting requestParameters.ruleAction to “allow” and requestParameters.aclProtocol to “-1”.
If not opening all ports the attacker creates ACL rule to allow all inbound traffic on ports with range larger than 1024 setting the requestParameters.ruleAction to “allow”, and requestParameters.portRange.to - requestParameters.portRange.from > 1024.
The attacker associates the modified or newly created ACL with one or more subnets within the VPC.
The attacker attempts to connect to resources within the protected subnets using various protocols and ports to validate access.
Upon successful connection, the attacker can access and exfiltrate data, deploy malicious code, or disrupt services within the targeted subnets.

Impact

A successful attack exploiting an overly permissive Network ACL can lead to unrestricted access to systems and data within the affected AWS subnets. This could result in data breaches, service disruption, or the deployment of ransomware. The number of affected resources depends on the scope of the ACL and the number of subnets it protects. The impact can range from a single compromised EC2 instance to a complete compromise of the AWS environment.

Recommendation

Deploy the Sigma rule AWS Network ACL Created with All Open Ports to your SIEM and tune for your environment to detect the creation of overly permissive ACLs.
Enable AWS CloudTrail logging for all regions in your AWS account to ensure complete visibility into API activity (AWS CloudTrail CreateNetworkAclEntry, AWS CloudTrail ReplaceNetworkAclEntry).
Implement infrastructure-as-code (IaC) practices and automated validation to prevent the creation of overly permissive ACLs.
Regularly review existing Network ACLs to identify and remediate any overly permissive rules.
Enforce the principle of least privilege when configuring Network ACLs, granting access only to the required ports and protocols.