diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index b50930676..3174261a9 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -414,8 +414,16 @@ module ApplicationHelper
   end
 
   def format_activity_description(text)
-    h(text.to_s.truncate(240).gsub(%r{[\r\n]*<(pre|code)>.*$}m, '...')).
-      gsub(/[\r\n]+/, "<br />").html_safe
+    h(
+      # Limit input to avoid regex performance issues
+      text.to_s.slice(0, 10240)
+      # Abbreviate consecutive quoted lines as '> ...', keeping the first line
+      .gsub(%r{(^>.*?(?:\r?\n))(?:>.*?(?:\r?\n)+)+}m, "\\1> ...\n")
+      # Remove all content following the first <pre> or <code> tag
+      .sub(%r{[\r\n]*<(pre|code)>.*$}m, '')
+      # Truncate the description to a specified length and append '...'
+      .truncate(240)
+    ).gsub(/[\r\n]+/, "<br>").html_safe
   end
 
   def format_version_name(version)
diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index 9f2eb8405..31c87daea 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -2329,6 +2329,35 @@ class ApplicationHelperTest < Redmine::HelperTest
     end
   end
 
+  def test_format_activity_description_should_strip_quoted_text
+    text = <<~TEXT
+      John Smith wrote in #note-1:
+      > The quick brown fox
+      > jumps over the lazy dog.
+
+      Brick quiz whangs jumpy veldt fox.
+
+      > The five
+
+      > boxing wizards
+
+      > jump quickly.
+
+      The quick onyx goblin jumps over the lazy dwarf.
+    TEXT
+
+    expected =
+      'John Smith wrote in #note-1:<br>' \
+      '&gt; The quick brown fox<br>' \
+      '&gt; ...<br>' \
+      'Brick quiz whangs jumpy veldt fox.<br>' \
+      '&gt; The five<br>' \
+      '&gt; ...<br>' \
+      'The quick onyx goblin jumps over the lazy dwarf.<br>'
+
+    assert_equal expected, format_activity_description(text)
+  end
+
   private
 
   def wiki_links_with_special_characters