diff --git a/lib/fluent/plugin/parser_syslog.rb b/lib/fluent/plugin/parser_syslog.rb
index acf2cbfa71..2b6fcca479 100644
--- a/lib/fluent/plugin/parser_syslog.rb
+++ b/lib/fluent/plugin/parser_syslog.rb
@@ -44,7 +44,7 @@ class SyslogParser < Parser
       RFC3164_CAPTURES = RFC3164_WITHOUT_TIME_AND_PRI_REGEXP.names.freeze
       RFC3164_PRI_REGEXP = /^<(?<pri>[0-9]{1,3})>/
 
-      RFC5424_WITHOUT_TIME_AND_PRI_REGEXP = /(?<host>[!-~]{1,255}) (?<ident>[!-~]{1,48}) (?<pid>[!-~]{1,128}) (?<msgid>[!-~]{1,32}) (?<extradata>(?:\-|(?:\[.*?(?<!\\)\])+))(?: (?<message>.+))?\z/m
+      RFC5424_WITHOUT_TIME_AND_PRI_REGEXP = /(?<host>[!-~]{1,255}) (?<ident>[!-~]{1,48}) (?<pid>[!-~]{1,128}) (?<msgid>[!-~]{1,32}) (?<extradata>(?:\-|(?:\[.*?(?<!\\)\])))(?: (?<message>.+))?\z/m
       RFC5424_CAPTURES = RFC5424_WITHOUT_TIME_AND_PRI_REGEXP.names.freeze
       RFC5424_PRI_REGEXP = /^<(?<pri>\d{1,3})>\d\d{0,2}\s/
 
diff --git a/test/plugin/test_parser_syslog.rb b/test/plugin/test_parser_syslog.rb
index 64161f48f7..dcdbca8388 100644
--- a/test/plugin/test_parser_syslog.rb
+++ b/test/plugin/test_parser_syslog.rb
@@ -1,6 +1,7 @@
 require_relative '../helper'
 require 'fluent/test/driver/parser'
 require 'fluent/plugin/parser'
+require 'timeout'
 
 class SyslogParserTest < ::Test::Unit::TestCase
   def setup
@@ -199,6 +200,16 @@ def test_parse_various_characters_for_tag_with_priority(param)
   end
 
   class TestRFC5424Regexp < self
+    def test_rejects_invalid_structured_data_without_excessive_backtracking
+      text = 'host ident pid msgid ' + ('[example]' * 30) + 'invalid'
+
+      match = Timeout.timeout(1) do
+        Fluent::Plugin::SyslogParser::RFC5424_WITHOUT_TIME_AND_PRI_REGEXP.match(text)
+      end
+
+      assert_nil(match)
+    end
+
     data('regexp' => 'regexp', 'string' => 'string')
     def test_parse_with_rfc5424_message(param)
       @parser.configure(