Fix Mastodon not correctly processing HTTP Signatures with query strings (#28476)

app/controllers/concerns/signature_verification.rb

@@ -91,14 +91,23 @@ module SignatureVerification
     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
+    compare_signed_string = build_signed_string(include_query_string: true)
 
     return actor unless verify_signature(actor, signature, compare_signed_string).nil?
 
+    # Compatibility quirk with older Mastodon versions
+    compare_signed_string = build_signed_string(include_query_string: false)
+    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?
 
+    compare_signed_string = build_signed_string(include_query_string: true)
+    return actor unless verify_signature(actor, signature, compare_signed_string).nil?
+
+    # Compatibility quirk with older Mastodon versions
+    compare_signed_string = build_signed_string(include_query_string: false)
     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']
@@ -180,11 +189,18 @@ module SignatureVerification
     nil
   end
 
-  def build_signed_string
+  def build_signed_string(include_query_string: true)
     signed_headers.map do |signed_header|
       case signed_header
       when Request::REQUEST_TARGET
-        "#{Request::REQUEST_TARGET}: #{request.method.downcase} #{request.path}"
+        if include_query_string
+          "#{Request::REQUEST_TARGET}: #{request.method.downcase} #{request.original_fullpath}"
+        else
+          # Current versions of Mastodon incorrectly omit the query string from the (request-target) pseudo-header.
+          # Therefore, temporarily support such incorrect signatures for compatibility.
+          # TODO: remove eventually some time after release of the fixed version
+          "#{Request::REQUEST_TARGET}: #{request.method.downcase} #{request.path}"
+        end
       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?

app/lib/request.rb

@@ -77,6 +77,7 @@ class Request
     @url         = Addressable::URI.parse(url).normalize
     @http_client = options.delete(:http_client)
     @allow_local = options.delete(:allow_local)
+    @full_path   = options.delete(:with_query_string)
     @options     = options.merge(socket_class: use_proxy? || @allow_local ? ProxySocket : Socket)
     @options     = @options.merge(timeout_class: PerOperationWithDeadline, timeout_options: TIMEOUT)
     @options     = @options.merge(proxy_url) if use_proxy?
@@ -146,7 +147,7 @@ class Request
   private
 
   def set_common_headers!
-    @headers[REQUEST_TARGET]    = "#{@verb} #{@url.path}"
+    @headers[REQUEST_TARGET]    = request_target
     @headers['User-Agent']      = Mastodon::Version.user_agent
     @headers['Host']            = @url.host
     @headers['Date']            = Time.now.utc.httpdate
@@ -157,6 +158,14 @@ class Request
     @headers['Digest'] = "SHA-256=#{Digest::SHA256.base64digest(@options[:body])}"
   end
 
+  def request_target
+    if @url.query.nil? || !@full_path
+      "#{@verb} #{@url.path}"
+    else
+      "#{@verb} #{@url.path}?#{@url.query}"
+    end
+  end
+
   def signature
     algorithm = 'rsa-sha256'
     signature = Base64.strict_encode64(@keypair.sign(OpenSSL::Digest.new('SHA256'), signed_string))