0x00 概述
CobaltStrike是一款内网渗透的商业远控软件，支持自定义脚本扩展，功能非常强大。前段时间Github上有好心人放出了CobaltStrike3.12的试用版，接着Lz1y很快就放出了破解版，加上热心老哥提供了的xor64.bin（试用版中没有这个文件），一个比较完美的最新可用版本诞生了。下面我们看下最新试用版是如何被完美破解的。
0x02 上手
CobaltStrike（下面简称CS）主体代码是用Java开发的，逆起来比较友好。用jd-gui反编译cobaltstrike.jar文件，可以看到代码几乎没有做防破解。Java源码没有任何混淆。但是查看反编译的源码时，很多地方出现了// INTERNAL ERROR //，这里我推荐一款Java反编译工具luyten，几乎可以100%反编译获得cobaltstrike.jar源码。
CS的License处理逻辑在common/License.java文件中：
package common;
import aggressor.*;
import javax.swing.*;
import java.awt.*;
public class License
{
private static long life;
private static long today;
private static long start;
private static long difference;
private static long getTimeSinceStart() {
final Prefs options = Prefs.getPreferences();
License.today = System.currentTimeMillis();
License.start = options.getLongNumber("cobaltstrike.start.int", 0L);
if (License.start == 0L) {
options.set("cobaltstrike.start.int", License.today + "");
options.save();
License.start = License.today;
}
return License.difference = (License.today - License.start) / 86400000L;
}
public static void checkLicenseGUI(final Authorization auth) {
getTimeSinceStart();
if (License.difference > License.life || License.today - License.start < 0L) {
JOptionPane.showMessageDialog(null, "Your Cobalt Strike trial is now expired.
Please purchase a license and use the
software update feature to continue.
For details, visit:
https://www.cobaltstrike.com/", null, 0);
System.exit(0);
}
else {
final long left = License.life - License.difference;
String form = left + " day";
if (left != 1L) {
form += "s";
}
CommonUtils.print_warn("This is a trial version of Cobalt Strike. You have " + form + " left of your trial. If you purchased Cobalt Strike. Run the Update program and enter your license.");
CommonUtils.print_trial("WARNING! This trial is *built* to get caught by standard defenses. The licensed product does not have these restrictions. See: http://blog.cobaltstrike.com/2015/10/14/the-cobalt-strike-trials-evil-bit/");
JOptionPane.showMessageDialog(null, "This is a trial version of Cobalt Strike.
You have " + form + " left of your trial.
If you purchased Cobalt Strike. Run the
Update program and enter your license.", null, 1);
}
}
public static boolean isTrial() {
return true;
}
public static void checkLicenseConsole(final Authorization auth) {
getTimeSinceStart();
if (License.difference > License.life || License.today - License.start < 0L) {
CommonUtils.print_error("Your Cobalt Strike trial is now expired. Please purchase a license and use the software update feature to continue. For details, visit: https://www.cobaltstrike.com/");
System.exit(0);
}
else {
final long left = License.life - License.difference;
String form = left + " day";
if (left != 1L) {
form += "s";
}
CommonUtils.print_warn("This is a trial version of Cobalt Strike. You have " + form + " left of your trial. If you purchased Cobalt Strike. Run the Update program and enter your license.");
CommonUtils.print_trial("WARNING! This trial is *built* to get caught by standard defenses. The licensed product does not have these restrictions. See: http://blog.cobaltstrike.com/2015/10/14/the-cobalt-strike-trials-evil-bit/");
}
}
static {
License.life = 21L;
License.today = 0L;
License.start = 0L;
License.difference = 0L;
}
}
代码逻辑很清晰，这里我们有两个方向进行patch：
- 修改
License.life无限延长试用 - 修改
isTrial()返回值，伪造成正式版
因为CS很多地方的试用版和正式版处理逻辑不同，所以修改了isTrial()返回值之后，我们还需要修改所有调用了isTrial()函数的地方，对代码进行调整。另外试用版CS留了一些特征指纹和限制，我们也需要去除相应的特征代码。
修改重打包
既然知道了破解思路，我们看下如何动手操作去修改源码并重编译。Java编程中我们可以使用jar工具将一系列的.class文件打包成jar包，供其他java程序使用。我们也可以修改jar包中.class文件的内容，并重新编译打包。比如修改demo.jar中的example.class并重新编译的过程如下：
-
使用jd-gui、luyten等工具把demo.jar包中的class反编译成源码，从中提取得到example.java
-
执行
jar xvf demo.jar解压demo.jar得到jar包的子文件（注意会解压到当前目录），将example.java文件放置到与example.class文件同一目录 -
执行
javac -cp a.jar;b.jar;c.jar example.java重新编译。(或者javac -cp demo.jar example.java)得到新的example.class文件。其中a.jar、b.jar、c.jar是依赖包，一般直接依赖一个原始解压的demo.jar包即可
-
确保编译后的example.class替换了原来的example.class文件（可以通过jd-gui反编译查看）
-
执行
jar -uvf demo.jar com/some/path/example.class更新demo.jar包
更新jar包中的class文件时，新的class文件目录路径需要与原package路径保持一致。比如修改了aggressor.AggressorClient.java并重新编译之后，更新jar包的命令如下：
KINGX modified_java_files >jar -uvf cobaltstrike-with-xor64.jar aggressor/AggressorClient*.class 正在添加: aggressor/AggressorClient$1.class(输入 = 650) (输出 = 403)(压缩了 38%) 正在添加: aggressor/AggressorClient$2.class(输入 = 1263) (输出 = 704)(压缩了 44%) 正在添加: aggressor/AggressorClient.class(输入 = 11115) (输出 = 5196)(压缩了 53%)
可能遇到的问题
修改后的java文件在重新编译为class文件时，可能会遇到很多奇怪的报错。有时候是因为反编译出的源码存在错误导致的，这个时候我们可以将luyten、jad、jd-gui等反编译工具结合使用，尽量还原成正确的源码，再重新编译。 比如：AggressorClient.java，jad aggressor/AggressorClient*.class和luyten反编译得到的源码是不一样的。
0x03 试用版Patch详细分析
Tips: 以下代码片段中行首的 - 代表删除，+ 代表新增
Patch 试用版本
修改common.License，去掉checkLicenseGUI()、checkLicenseConsole()函数体，修改isTrial()返回值为true
修改主程序标题
aggressor.AggressorClient，修改getTitle()函数
解除listener同类数量限制
一个teamserver默认只能监听一个listener，可以通过修改代码去除限制。
aggressor.dialogs.ListenerDialog，去除以下代码：
...
else if (Listener.isEgressBeacon(payload) && DataUtils.isBeaconDefined(this.datal) && !name.equals(DataUtils.getEgressBeaconListener(this.datal))) {
DialogUtils.showError("You may only define one egress Beacon per team server.
There are a few things I need to sort before you can
put multiple Beacon HTTP/DNS listeners on one server.
Spin up a new team server and add your listener there.");
}
...
3.去除EICAR后门指纹特征
试用版有几个地方存在EICAR特征字符：X5O!P%@AP[4PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*，都需要进行清理：
common.ListenerConfig
修改pad()函数：
result.append("5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*u0000");
result.append("123u0000");
resources/template.x64.ps1、resources/template.x86.ps1
$eicar = 'X5O!P%@AP[4PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*' $eicar = ''
server.ProfileEdits
c2profile.addCommand(".http-get.server", "!header", "X-Malware: X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*");
c2profile.addCommand(".http-post.server", "!header", "X-Malware: X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*");
c2profile.addCommand(".http-stager.server", "!header", "X-Malware: X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*");
c2profile.addCommand(".stage.transform-x86", "append", "X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*");
c2profile.addCommand(".stage.transform-x64", "append", "X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*");
common.ArtifactUtils
因为已经修改了License.isTrial()返回值为false，所以下面这段改不改也没什么影响。
if (License.isTrial()) {
packer.addString("X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*");
CommonUtils.print_trial("Added EICAR string to " + s);
}
添加XOR64.BIN
生成payload时，会调用common.ArtifactUtils中的XorEncode()进行编码：
public static byte[] _XorEncode(final byte[] data, final String arch) {
AssertUtils.TestArch(arch);
if ("x86".equals(arch)) {
final byte[] decoder = XorStub();
final byte[] payload = XorEncoder.encode(data);
return CommonUtils.join(decoder, payload);
}
if ("x64".equals(arch)) {
final byte[] decoder = CommonUtils.readResource("resources/xor64.bin");
final byte[] payload = XorEncoder.encode(data);
return CommonUtils.join(decoder, payload);
}
return new byte[0];
}
public static byte[] XorEncode(final byte[] data, final String arch) {
if (License.isTrial()) {
CommonUtils.print_trial("Disabled " + arch + " payload stage encoding.");
return data;
}
AssertUtils.Test(data.length > 16384, "XorEncode used on a stager (or some other small thing)");
return _XorEncode(data, arch);
}
试用版不会进行payload stage encoding，所以试用版软件包中并没有带xor.bin/xor64.bin文件，如果有这两个文件的话，可以添加到resources/xor.bin、resources/xor64.bin路径下。Github上有热心老哥提供了xor64的生成脚本：https://github.com/verctor/CS_xor64
源码逐个修改完，重新编译更新到cobaltstrike.jar包中，再拷贝替换掉原版的jar包就OK了。