diff --git a/sentry-ruby/lib/sentry/data_collection.rb b/sentry-ruby/lib/sentry/data_collection.rb
index 60ca15920..601eda599 100644
--- a/sentry-ruby/lib/sentry/data_collection.rb
+++ b/sentry-ruby/lib/sentry/data_collection.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "sentry/data_collection/key_value_collection"
+
 module Sentry
   class DataCollection
     # Configuration for the categories of data collected by the SDK.
@@ -34,25 +36,6 @@ class DataCollection
     outgoing_response
     ].freeze
 
-    # Configuration for key-value data collection.
-    class KeyValueCollection
-      # `mode` controls whether values are collected:
-      # - `:off` disables collection.
-      # - `:deny_list` collects values except those matching `terms`.
-      # - `:allow_list` collects only values matching `terms`.
-      # @return [:off, :deny_list, :allow_list]
-      attr_accessor :mode
-
-      # `terms` contains the keys or patterns used by the selected mode.
-      # @return [Array<String>, nil]
-      attr_accessor :terms
-
-      def initialize(mode:, terms:)
-        @mode = mode
-        @terms = terms
-      end
-    end
-
     class HttpHeaders
       # @return [KeyValueCollection]
       attr_accessor :request
diff --git a/sentry-ruby/lib/sentry/data_collection/key_value_collection.rb b/sentry-ruby/lib/sentry/data_collection/key_value_collection.rb
new file mode 100644
index 000000000..88d967b91
--- /dev/null
+++ b/sentry-ruby/lib/sentry/data_collection/key_value_collection.rb
@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+module Sentry
+  class DataCollection
+    # Configuration for key-value data collection.
+    class KeyValueCollection
+      FILTERED_VALUE = "[Filtered]"
+
+      # Key name fragments whose values must never be sent in plaintext.
+      module SensitiveDenylist
+        TERMS = %w[
+          auth
+          token
+          secret
+          password
+          passwd
+          pwd
+          key
+          jwt
+          bearer
+          sso
+          saml
+          csrf
+          xsrf
+          credentials
+          session
+          sid
+          identity
+        ].freeze
+      end
+
+      # `mode` controls whether values are collected:
+      # - `:off` disables collection.
+      # - `:deny_list` collects values except those matching `terms`.
+      # - `:allow_list` collects only values matching `terms`.
+      # @return [:off, :deny_list, :allow_list]
+      attr_accessor :mode
+
+      # `terms` contains the keys or patterns used by the selected mode.
+      # @return [Array<String>, nil]
+      attr_accessor :terms
+
+      def initialize(mode:, terms:)
+        @mode = mode
+        @terms = terms
+      end
+
+      # Applies this collection configuration without changing the input hash.
+      # Keys are retained whenever the category is collected; values that are not
+      # safe to send are replaced with FILTERED_VALUE.
+      #
+      # @param values [Hash] key-value data to filter
+      # @return [Hash] a new filtered hash, or an empty hash when collection is off
+      def filter(values)
+        return {} if mode == :off
+
+        values.each_with_object({}) do |(key, value), filtered|
+          filtered[key] = safe_value?(key) ? value : FILTERED_VALUE
+        end
+      end
+
+      private
+
+      def safe_value?(key)
+        key_name = key.to_s
+        return false if sensitive?(key_name)
+
+        case mode
+        when :deny_list
+          !matches_any_term?(key_name, terms)
+        when :allow_list
+          matches_any_term?(key_name, terms)
+        else
+          false
+        end
+      end
+
+      def sensitive?(key)
+        matches_any_term?(key, SensitiveDenylist::TERMS)
+      end
+
+      def matches_any_term?(key, terms)
+        Array(terms).any? { |term| key.downcase.include?(term.to_s.downcase) }
+      end
+    end
+  end
+end
diff --git a/sentry-ruby/spec/sentry/data_collection/key_value_collection_spec.rb b/sentry-ruby/spec/sentry/data_collection/key_value_collection_spec.rb
new file mode 100644
index 000000000..ae3f4de50
--- /dev/null
+++ b/sentry-ruby/spec/sentry/data_collection/key_value_collection_spec.rb
@@ -0,0 +1,94 @@
+# frozen_string_literal: true
+
+require "sentry/data_collection/key_value_collection"
+
+RSpec.describe Sentry::DataCollection::KeyValueCollection do
+  subject(:collection) { described_class.new(mode: mode, terms: terms) }
+
+  let(:values) do
+    {
+      "Authorization" => "secret-token",
+      "page" => "2",
+      "display_name" => "Ada",
+      42 => "numeric key"
+    }
+  end
+  let(:mode) { :deny_list }
+  let(:terms) { nil }
+
+  describe "#filter" do
+    it "uses the collection configuration" do
+      expect(collection.filter(values)).to eq(
+        "Authorization" => "[Filtered]",
+        "page" => "2",
+        "display_name" => "Ada",
+        42 => "numeric key"
+      )
+    end
+
+    context "when mode is :off" do
+      let(:mode) { :off }
+
+      it "does not collect keys or values" do
+        expect(collection.filter(values)).to eq({})
+      end
+    end
+
+    context "when mode is :deny_list" do
+      it "matches sensitive terms partially and case-insensitively" do
+        expect(described_class.new(mode: :deny_list, terms: nil).filter(
+          { "X-Auth-Token" => "a", "ACCESS_SECRET_VALUE" => "b", "sideline" => "c" }
+        )).to eq(
+          "X-Auth-Token" => "[Filtered]",
+          "ACCESS_SECRET_VALUE" => "[Filtered]",
+          "sideline" => "[Filtered]"
+        )
+      end
+
+      it "applies additional deny terms" do
+        expect(described_class.new(mode: :deny_list, terms: ["USER", :internal]).filter(
+          { "user_id" => "1", "internal" => "value" }
+        )).to eq(
+          "user_id" => "[Filtered]",
+          "internal" => "[Filtered]"
+        )
+      end
+
+      it "covers every built-in sensitive term" do
+        values = Sentry::DataCollection::KeyValueCollection::SensitiveDenylist::TERMS.to_h do |term|
+          ["prefix-#{term.upcase}-suffix", "value"]
+        end
+
+        expect(collection.filter(values).values.uniq).to eq(["[Filtered]"])
+      end
+    end
+
+    context "when mode is :allow_list" do
+      let(:mode) { :allow_list }
+      let(:terms) { ["page", "display"] }
+
+      it "filters values whose keys are not allowed" do
+        expect(collection.filter(values)).to eq(
+          "Authorization" => "[Filtered]",
+          "page" => "2",
+          "display_name" => "Ada",
+          42 => "[Filtered]"
+        )
+      end
+
+      it "still filters sensitive keys listed in the allow list" do
+        expect(described_class.new(mode: :allow_list, terms: ["token", "public"]).filter(
+          { "token" => "secret", "public" => "value" }
+        )).to eq("token" => "[Filtered]", "public" => "value")
+      end
+    end
+
+    it "does not mutate the input" do
+      original = values.dup
+
+      collection.filter(values)
+
+      expect(values).to eq(original)
+    end
+  end
+end