diff --git a/middleware/security_context_setter.rb b/middleware/security_context_setter.rb
index 06a24deec0c..3321fbafbac 100644
--- a/middleware/security_context_setter.rb
+++ b/middleware/security_context_setter.rb
@@ -22,7 +22,7 @@ def call(env)
         security_context_configurer = @security_context_configurer
 
         if request_path && request_path.match(UPLOADS_PATH_REGEX)
-          upload_start_time = Rack::Request.new(env).params['upload_start_time'].to_i
+          upload_start_time = upload_start_time_from_nginx(env)
           if upload_start_time
             relaxed_token_decoder = VCAP::CloudController::UaaTokenDecoder.new(VCAP::CloudController::Config.config.get(:uaa), alternate_reference_time: upload_start_time)
             security_context_configurer = VCAP::CloudController::Security::SecurityContextConfigurer.new(relaxed_token_decoder)
@@ -56,6 +56,16 @@ def call(env)
 
       private
 
+      def upload_start_time_from_nginx(env)
+        raw_value = Rack::Request.new(env).POST['upload_start_time']
+        return false if raw_value.blank?
+
+        upload_start_time = raw_value.to_i
+        return false unless upload_start_time.positive?
+
+        [upload_start_time, Time.now.to_i].min
+      end
+
       def id_from_token
         VCAP::CloudController::SecurityContext.token['user_id'] || VCAP::CloudController::SecurityContext.token['client_id']
       end
diff --git a/spec/unit/middleware/security_context_setter_spec.rb b/spec/unit/middleware/security_context_setter_spec.rb
index 6031b6e36ee..6bfe35a5d15 100644
--- a/spec/unit/middleware/security_context_setter_spec.rb
+++ b/spec/unit/middleware/security_context_setter_spec.rb
@@ -181,6 +181,85 @@ module Middleware
             expect { middleware.call(env) }.to raise_error(error)
           end
         end
+
+        context 'when the request targets an upload endpoint' do
+          let(:path_info) { '/v3/packages/0b6a2f0e-9c5a-4c1d-8e2f-1a2b3c4d5e6f/upload' }
+          let(:upload_env) do
+            {
+              'HTTP_AUTHORIZATION' => 'auth-token',
+              'PATH_INFO' => path_info,
+              'REQUEST_PATH' => path_info,
+              'REQUEST_METHOD' => 'POST',
+              'QUERY_STRING' => query_string,
+              'CONTENT_TYPE' => content_type,
+              'rack.input' => StringIO.new(request_body)
+            }
+          end
+          let(:query_string) { '' }
+          let(:content_type) { 'application/x-www-form-urlencoded' }
+          let(:request_body) { '' }
+
+          context 'when upload_start_time is absent from the POST body' do
+            it 'uses the strict token decoder' do
+              expect(VCAP::CloudController::UaaTokenDecoder).not_to receive(:new)
+
+              middleware.call(upload_env)
+            end
+          end
+
+          context 'when upload_start_time is passed as a query parameter (client-supplied, ignored)' do
+            let(:query_string) { 'upload_start_time=123' }
+
+            it 'ignores it and uses the strict token decoder' do
+              expect(VCAP::CloudController::UaaTokenDecoder).not_to receive(:new)
+
+              middleware.call(upload_env)
+            end
+          end
+
+          context 'when upload_start_time is in the POST body (as injected by nginx upload module)' do
+            let(:request_body) { 'upload_start_time=123' }
+
+            it 'uses a relaxed token decoder with the given reference time' do
+              expect(VCAP::CloudController::UaaTokenDecoder).to receive(:new).
+                with(anything, alternate_reference_time: 123).and_return(token_decoder)
+
+              middleware.call(upload_env)
+            end
+          end
+
+          context 'when upload_start_time in the POST body is in the future' do
+            let(:request_body) { 'upload_start_time=9999999999' }
+
+            it 'clamps the reference time to now' do
+              Timecop.freeze do
+                expect(VCAP::CloudController::UaaTokenDecoder).to receive(:new).
+                  with(anything, alternate_reference_time: Time.now.to_i).and_return(token_decoder)
+                middleware.call(upload_env)
+              end
+            end
+          end
+
+          context 'when upload_start_time in the POST body is not a positive integer' do
+            let(:request_body) { 'upload_start_time=abc' }
+
+            it 'uses the strict token decoder' do
+              expect(VCAP::CloudController::UaaTokenDecoder).not_to receive(:new)
+
+              middleware.call(upload_env)
+            end
+          end
+
+          context 'when upload_start_time in the POST body is empty' do
+            let(:request_body) { 'upload_start_time=' }
+
+            it 'uses the strict token decoder' do
+              expect(VCAP::CloudController::UaaTokenDecoder).not_to receive(:new)
+
+              middleware.call(upload_env)
+            end
+          end
+        end
       end
     end
   end