Base64

Created the Monday 18 March 2019. Updated 1 year, 6 months ago.

Base64 is a simple encoding scheme that is often used by malware to represent binary data in an ASCII string. This allows the malware to encode and transmit binary data, such as a payload or network traffic, in a way that is more compact and easier to transmit over text-based communication channels.

Base64 uses a 64-character alphabet to encode the data, which includes the upper and lower case letters, the digits 0-9, and the symbols "+" and "/". The encoded data is typically padded with the character "=" to ensure that it has a length that is a multiple of 4. The encoded data can then be decoded using the same 64-character alphabet to recover the original binary data. This makes Base64 a useful tool for malware to conceal their payloads and communicate with their command and control (C2) servers.

Technique Identifiers

U0706 E1027.m02

Technique Tags

Base64 Binary data ASCII string Encoding Text-based communication channels 64-character alphabet Padded

Code Snippets

Description

This Go program uses the Base64 encoding scheme to encode and decode a string. The program takes a single command line argument, which is the string to be encoded and decoded. The program first uses the base64 package to encode the string using the Standard encoding alphabet. The encoded string is then printed to the screen. The program then decodes the encoded string using the same alphabet, and prints the resulting decoded string to the screen. This example demonstrates how the Base64 encoding scheme can be used to encode and decode binary data in a compact and easily transmitted format. In the context of malware, this technique can be used to conceal payloads or encode network communication in order to avoid detection and analysis.

package main

import (
    "encoding/base64"
    "fmt"
    "os"
)

func main() {

    arg1 := os.Args[1]

    encoded := base64.StdEncoding.EncodeToString([]byte(arg1))
    fmt.Println(encoded)

    decoded, err := base64.StdEncoding.DecodeString(encoded)
    if err != nil {
        panic("error")
    }
    fmt.Println(string(decoded))
}

About Author Open Snippet

Author: Thomas Roccia (fr0gger) / Target Platform: Windows

Detection Rules

rule golang_base64_enc {
	meta:
		author = "RussianPanda"
		decription = "Detects Base64 Encoding and Decoding patterns in Golang binaries"
        	reference = "https://unprotect.it/technique/base64/"
		date = "1/10/2024"
		hash = "509a359b4d0cd993497671b91255c3775628b078cde31a32158c1bc3b2ce461c"
	strings:
	        $s1 = {62 61 73 65 36 34 2e 53 74 64 45 6e 63 6f 64 69 6e 67 2e 45 6e 63 6f 64 65 54 6f 53 74 72 69 6e 67 28 [0-15] 29}
	        $s2 = {62 61 73 65 36 34 2e 53 74 64 45 6e 63 6f 64 69 6e 67 2e 44 65 63 6f 64 65 53 74 72 69 6e 67 28 [0-15] 29}
	        $s3 = {69 66 20 65 72 72 20 21 3D 20 6E 69 6C 20 7B}
		$s4 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
 	condition:
		all of ($s*) 
        	and uint16(0) == 0x5A4D
}


rule base64_enc {
	meta:
		author = "RussianPanda"
		decription = "Detects Base64 Encoding"
        	reference = "https://unprotect.it/technique/base64/"
		date = "1/10/2024"
		hash = "09506d1af5d8e6570b2b7d05143f444f5685d2a9f3304780ef376edf7b2d79e6"
	strings:
		$s2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
        	$s3 = {83 E? 3F}
 	condition:
		all of ($s*) 
        	and uint16(0) == 0x5A4D
		
}

Contributors

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

https://medium.com/@bromiley/malware-monday-obfuscation-f65239146db0

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