# frozen_string_literal: true # Implemented according to HTTP signatures (Draft 6) # <https://tools.ietf.org/html/draft-cavage-http-signatures-06> module SignatureVerification extend ActiveSupport::Concern include DomainControlHelper EXPIRATION_WINDOW_LIMIT = 12.hours CLOCK_SKEW_MARGIN = 1.hour class SignatureVerificationError < StandardError; end class SignatureParamsParser < Parslet::Parser rule(:token) { match("[0-9a-zA-Z!#$%&'*+.^_`|~-]").repeat(1).as(:token) } rule(:quoted_string) { str('"') >> (qdtext | quoted_pair).repeat.as(:quoted_string) >> str('"') } # qdtext and quoted_pair are not exactly according to spec but meh rule(:qdtext) { match('[^\\\\"]') } rule(:quoted_pair) { str('\\') >> any } rule(:bws) { match('\s').repeat } rule(:param) { (token.as(:key) >> bws >> str('=') >> bws >> (token | quoted_string).as(:value)).as(:param) } rule(:comma) { bws >> str(',') >> bws } # Old versions of node-http-signature add an incorrect "Signature " prefix to the header rule(:buggy_prefix) { str('Signature ') } rule(:params) { buggy_prefix.maybe >> (param >> (comma >> param).repeat).as(:params) } root(:params) end class SignatureParamsTransformer < Parslet::Transform rule(params: subtree(:param)) do (param.is_a?(Array) ? param : [param]).each_with_object({}) { |(key, value), hash| hash[key] = value } end rule(param: { key: simple(:key), value: simple(:val) }) do [key, val] end rule(quoted_string: simple(:string)) do string.to_s end rule(token: simple(:string)) do string.to_s end end def require_account_signature! render json: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_account end def require_actor_signature! render json: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_actor end def signed_request? request.headers['Signature'].present? end def signature_verification_failure_reason @signature_verification_failure_reason end def signature_verification_failure_code @signature_verification_failure_code || 401 end def signature_key_id signature_params['keyId'] rescue SignatureVerificationError nil end def signed_request_account signed_request_actor.is_a?(Account) ? signed_request_actor : nil end def signed_request_actor return @signed_request_actor if defined?(@signed_request_actor) raise SignatureVerificationError, 'Request not signed' unless signed_request? raise SignatureVerificationError, 'Incompatible request signature. keyId and signature are required' if missing_required_signature_parameters? raise SignatureVerificationError, 'Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)' unless %w(rsa-sha256 hs2019).include?(signature_algorithm) raise SignatureVerificationError, 'Signed request date outside acceptable time window' unless matches_time_window? verify_signature_strength! verify_body_digest! actor = actor_from_key_id(signature_params['keyId']) raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if actor.nil? signature = Base64.decode64(signature_params['signature']) compare_signed_string = build_signed_string return actor unless verify_signature(actor, signature, compare_signed_string).nil? actor = stoplight_wrap_request { actor_refresh_key!(actor) } raise SignatureVerificationError, "Could not refresh public key #{signature_params['keyId']}" if actor.nil? return actor unless verify_signature(actor, signature, compare_signed_string).nil? fail_with! "Verification failed for #{actor.to_log_human_identifier} #{actor.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)", signed_string: compare_signed_string, signature: signature_params['signature'] rescue SignatureVerificationError => e fail_with! e.message rescue HTTP::Error, OpenSSL::SSL::SSLError => e fail_with! "Failed to fetch remote data: #{e.message}" rescue Mastodon::UnexpectedResponseError fail_with! 'Failed to fetch remote data (got unexpected reply from server)' rescue Stoplight::Error::RedLight fail_with! 'Fetching attempt skipped because of recent connection failure' end def request_body @request_body ||= request.raw_post end private def fail_with!(message, **options) Rails.logger.debug { "Signature verification failed: #{message}" } @signature_verification_failure_reason = { error: message }.merge(options) @signed_request_actor = nil end def signature_params @signature_params ||= begin raw_signature = request.headers['Signature'] tree = SignatureParamsParser.new.parse(raw_signature) SignatureParamsTransformer.new.apply(tree) end rescue Parslet::ParseFailed raise SignatureVerificationError, 'Error parsing signature parameters' end def signature_algorithm signature_params.fetch('algorithm', 'hs2019') end def signed_headers signature_params.fetch('headers', signature_algorithm == 'hs2019' ? '(created)' : 'date').downcase.split end def verify_signature_strength! raise SignatureVerificationError, 'Mastodon requires the Date header or (created) pseudo-header to be signed' unless signed_headers.include?('date') || signed_headers.include?('(created)') raise SignatureVerificationError, 'Mastodon requires the Digest header or (request-target) pseudo-header to be signed' unless signed_headers.include?(Request::REQUEST_TARGET) || signed_headers.include?('digest') raise SignatureVerificationError, 'Mastodon requires the Host header to be signed when doing a GET request' if request.get? && !signed_headers.include?('host') raise SignatureVerificationError, 'Mastodon requires the Digest header to be signed when doing a POST request' if request.post? && !signed_headers.include?('digest') end def verify_body_digest! return unless signed_headers.include?('digest') raise SignatureVerificationError, 'Digest header missing' unless request.headers.key?('Digest') digests = request.headers['Digest'].split(',').map { |digest| digest.split('=', 2) }.map { |key, value| [key.downcase, value] } sha256 = digests.assoc('sha-256') raise SignatureVerificationError, "Mastodon only supports SHA-256 in Digest header. Offered algorithms: #{digests.map(&:first).join(', ')}" if sha256.nil? return if body_digest == sha256[1] digest_size = begin Base64.strict_decode64(sha256[1].strip).length rescue ArgumentError raise SignatureVerificationError, "Invalid Digest value. The provided Digest value is not a valid base64 string. Given digest: #{sha256[1]}" end raise SignatureVerificationError, "Invalid Digest value. The provided Digest value is not a SHA-256 digest. Given digest: #{sha256[1]}" if digest_size != 32 raise SignatureVerificationError, "Invalid Digest value. Computed SHA-256 digest: #{body_digest}; given: #{sha256[1]}" end def verify_signature(actor, signature, compare_signed_string) if actor.keypair.public_key.verify(OpenSSL::Digest.new('SHA256'), signature, compare_signed_string) @signed_request_actor = actor @signed_request_actor end rescue OpenSSL::PKey::RSAError nil end def build_signed_string signed_headers.map do |signed_header| case signed_header when Request::REQUEST_TARGET "#{Request::REQUEST_TARGET}: #{request.method.downcase} #{request.path}" when '(created)' raise SignatureVerificationError, 'Invalid pseudo-header (created) for rsa-sha256' unless signature_algorithm == 'hs2019' raise SignatureVerificationError, 'Pseudo-header (created) used but corresponding argument missing' if signature_params['created'].blank? "(created): #{signature_params['created']}" when '(expires)' raise SignatureVerificationError, 'Invalid pseudo-header (expires) for rsa-sha256' unless signature_algorithm == 'hs2019' raise SignatureVerificationError, 'Pseudo-header (expires) used but corresponding argument missing' if signature_params['expires'].blank? "(expires): #{signature_params['expires']}" else "#{signed_header}: #{request.headers[to_header_name(signed_header)]}" end end.join("\n") end def matches_time_window? created_time = nil expires_time = nil begin if signature_algorithm == 'hs2019' && signature_params['created'].present? created_time = Time.at(signature_params['created'].to_i).utc elsif request.headers['Date'].present? created_time = Time.httpdate(request.headers['Date']).utc end expires_time = Time.at(signature_params['expires'].to_i).utc if signature_params['expires'].present? rescue ArgumentError => e raise SignatureVerificationError, "Invalid Date header: #{e.message}" end expires_time ||= created_time + 5.minutes unless created_time.nil? expires_time = [expires_time, created_time + EXPIRATION_WINDOW_LIMIT].min unless created_time.nil? return false if created_time.present? && created_time > Time.now.utc + CLOCK_SKEW_MARGIN return false if expires_time.present? && Time.now.utc > expires_time + CLOCK_SKEW_MARGIN true end def body_digest @body_digest ||= Digest::SHA256.base64digest(request_body) end def to_header_name(name) name.split('-').map(&:capitalize).join('-') end def missing_required_signature_parameters? signature_params['keyId'].blank? || signature_params['signature'].blank? end def actor_from_key_id(key_id) domain = key_id.start_with?('acct:') ? key_id.split('@').last : key_id if domain_not_allowed?(domain) @signature_verification_failure_code = 403 return end if key_id.start_with?('acct:') stoplight_wrap_request { ResolveAccountService.new.call(key_id.delete_prefix('acct:'), suppress_errors: false) } elsif !ActivityPub::TagManager.instance.local_uri?(key_id) account = ActivityPub::TagManager.instance.uri_to_actor(key_id) account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false, suppress_errors: false) } account end rescue Mastodon::PrivateNetworkAddressError => e raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})" rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteActorService::Error, ActivityPub::FetchRemoteKeyService::Error, Webfinger::Error => e raise SignatureVerificationError, e.message end def stoplight_wrap_request(&block) Stoplight("source:#{request.remote_ip}", &block) .with_threshold(1) .with_cool_off_time(5.minutes.seconds) .with_error_handler { |error, handle| error.is_a?(HTTP::Error) || error.is_a?(OpenSSL::SSL::SSLError) ? handle.call(error) : raise(error) } .run end def actor_refresh_key!(actor) return if actor.local? || !actor.activitypub? return actor.refresh! if actor.respond_to?(:refresh!) && actor.possibly_stale? ActivityPub::FetchRemoteActorService.new.call(actor.uri, only_key: true, suppress_errors: false) rescue Mastodon::PrivateNetworkAddressError => e raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})" rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteActorService::Error, Webfinger::Error => e raise SignatureVerificationError, e.message end end