diff --git a/modules/setting/server.go b/modules/setting/server.go
index cedca32da9..a865e942a6 100644
--- a/modules/setting/server.go
+++ b/modules/setting/server.go
@@ -370,6 +370,10 @@ func loadServerFrom(rootCfg ConfigProvider) {
 		}
 	}
 
+	// TODO: GOLANG-HTTP-TMPDIR: Some Golang packages (like "http") use os.TempDir() to create temporary files when uploading files.
+	// So ideally we should set the TMPDIR environment variable to make them use our managed temp directory.
+	// But there is no clear place to set it currently, for example: when running "install" page, the AppDataPath is not ready yet, then AppDataTempDir won't work
+
 	EnableGzip = sec.Key("ENABLE_GZIP").MustBool()
 	EnablePprof = sec.Key("ENABLE_PPROF").MustBool(false)
 	PprofDataPath = sec.Key("PPROF_DATA_PATH").MustString(filepath.Join(AppWorkPath, "data/tmp/pprof"))
diff --git a/modules/web/routemock.go b/modules/web/routemock.go
index e85b0db738..68d19475e9 100644
--- a/modules/web/routemock.go
+++ b/modules/web/routemock.go
@@ -46,11 +46,15 @@ func RouterMockPoint(pointName string) func(next http.Handler) http.Handler {
 //
 // Then the mock function will be executed as a middleware at the mock point.
 // It only takes effect in testing mode (setting.IsInTesting == true).
-func RouteMock(pointName string, h any) {
+func RouteMock(pointName string, h any) func() {
 	if _, ok := routeMockPoints[pointName]; !ok {
 		panic("route mock point not found: " + pointName)
 	}
+	old := routeMockPoints[pointName]
 	routeMockPoints[pointName] = toHandlerProvider(h)
+	return func() {
+		routeMockPoints[pointName] = old
+	}
 }
 
 // RouteMockReset resets all mock points (no mock anymore)
diff --git a/modules/web/router.go b/modules/web/router.go
index 5812ff69d4..5374f82a23 100644
--- a/modules/web/router.go
+++ b/modules/web/router.go
@@ -55,7 +55,7 @@ func NewRouter() *Router {
 // Use supports two middlewares
 func (r *Router) Use(middlewares ...any) {
 	for _, m := range middlewares {
-		if m != nil {
+		if !isNilOrFuncNil(m) {
 			r.chiRouter.Use(toHandlerProvider(m))
 		}
 	}
diff --git a/routers/common/middleware.go b/routers/common/middleware.go
index bfa258b976..6bf430d361 100644
--- a/routers/common/middleware.go
+++ b/routers/common/middleware.go
@@ -72,8 +72,13 @@ func RequestContextHandler() func(h http.Handler) http.Handler {
 			req = req.WithContext(cache.WithCacheContext(ctx))
 			ds.SetContextValue(httplib.RequestContextKey, req)
 			ds.AddCleanUp(func() {
-				if req.MultipartForm != nil {
-					_ = req.MultipartForm.RemoveAll() // remove the temp files buffered to tmp directory
+				// TODO: GOLANG-HTTP-TMPDIR: Golang saves the uploaded files to temp directory (TMPDIR) when parsing multipart-form.
+				// The "req" might have changed due to the new "req.WithContext" calls
+				// For example: in NewBaseContext, a new "req" with context is created, and the multipart-form is parsed there.
+				// So we always use the latest "req" from the data store.
+				ctxReq := ds.GetContextValue(httplib.RequestContextKey).(*http.Request)
+				if ctxReq.MultipartForm != nil {
+					_ = ctxReq.MultipartForm.RemoveAll() // remove the temp files buffered to tmp directory
 				}
 			})
 			next.ServeHTTP(respWriter, req)
diff --git a/routers/web/web.go b/routers/web/web.go
index 89a570dce0..6890789321 100644
--- a/routers/web/web.go
+++ b/routers/web/web.go
@@ -227,6 +227,8 @@ func ctxDataSet(args ...any) func(ctx *context.Context) {
 	}
 }
 
+const RouterMockPointBeforeWebRoutes = "before-web-routes"
+
 // Routes returns all web routes
 func Routes() *web.Router {
 	routes := web.NewRouter()
@@ -285,7 +287,7 @@ func Routes() *web.Router {
 
 	webRoutes := web.NewRouter()
 	webRoutes.Use(mid...)
-	webRoutes.Group("", func() { registerWebRoutes(webRoutes) }, common.BlockExpensive(), common.QoS())
+	webRoutes.Group("", func() { registerWebRoutes(webRoutes) }, common.BlockExpensive(), common.QoS(), web.RouterMockPoint(RouterMockPointBeforeWebRoutes))
 	routes.Mount("", webRoutes)
 	return routes
 }
diff --git a/services/context/base.go b/services/context/base.go
index de839ede81..8bd66bed09 100644
--- a/services/context/base.go
+++ b/services/context/base.go
@@ -43,8 +43,10 @@ type Base struct {
 	Locale translation.Locale
 }
 
+var ParseMultipartFormMaxMemory = int64(32 << 20)
+
 func (b *Base) ParseMultipartForm() bool {
-	err := b.Req.ParseMultipartForm(32 << 20)
+	err := b.Req.ParseMultipartForm(ParseMultipartFormMaxMemory)
 	if err != nil {
 		// TODO: all errors caused by client side should be ignored (connection closed).
 		if !errors.Is(err, io.EOF) && !errors.Is(err, io.ErrUnexpectedEOF) {
diff --git a/tests/integration/attachment_test.go b/tests/integration/attachment_test.go
index 44aaee09f8..18efde7214 100644
--- a/tests/integration/attachment_test.go
+++ b/tests/integration/attachment_test.go
@@ -7,17 +7,23 @@ import (
 	"bytes"
 	"image"
 	"image/png"
+	"io/fs"
 	"mime/multipart"
 	"net/http"
+	"os"
 	"strings"
 	"testing"
 
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/modules/storage"
 	"code.gitea.io/gitea/modules/test"
+	"code.gitea.io/gitea/modules/web"
+	route_web "code.gitea.io/gitea/routers/web"
+	"code.gitea.io/gitea/services/context"
 	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func testGeneratePngBytes() []byte {
@@ -52,14 +58,38 @@ func testCreateIssueAttachment(t *testing.T, session *TestSession, csrf, repoURL
 	return obj["uuid"]
 }
 
-func TestCreateAnonymousAttachment(t *testing.T) {
+func TestAttachments(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
+	t.Run("CreateAnonymousAttachment", testCreateAnonymousAttachment)
+	t.Run("CreateUser2IssueAttachment", testCreateUser2IssueAttachment)
+	t.Run("UploadAttachmentDeleteTemp", testUploadAttachmentDeleteTemp)
+	t.Run("GetAttachment", testGetAttachment)
+}
+
+func testUploadAttachmentDeleteTemp(t *testing.T) {
+	session := loginUser(t, "user2")
+	countTmpFile := func() int {
+		// TODO: GOLANG-HTTP-TMPDIR: Golang saves the uploaded file to os.TempDir() when it exceeds the max memory limit.
+		files, err := fs.Glob(os.DirFS(os.TempDir()), "multipart-*") //nolint:usetesting // Golang's "http" package's behavior
+		require.NoError(t, err)
+		return len(files)
+	}
+	var tmpFileCountDuringUpload int
+	defer test.MockVariableValue(&context.ParseMultipartFormMaxMemory, 1)()
+	defer web.RouteMock(route_web.RouterMockPointBeforeWebRoutes, func(resp http.ResponseWriter, req *http.Request) {
+		tmpFileCountDuringUpload = countTmpFile()
+	})()
+	_ = testCreateIssueAttachment(t, session, GetUserCSRFToken(t, session), "user2/repo1", "image.png", testGeneratePngBytes(), http.StatusOK)
+	assert.Equal(t, 1, tmpFileCountDuringUpload, "the temp file should exist when uploaded size exceeds the parse form's max memory")
+	assert.Equal(t, 0, countTmpFile(), "the temp file should be deleted after upload")
+}
+
+func testCreateAnonymousAttachment(t *testing.T) {
 	session := emptyTestSession(t)
 	testCreateIssueAttachment(t, session, GetAnonymousCSRFToken(t, session), "user2/repo1", "image.png", testGeneratePngBytes(), http.StatusSeeOther)
 }
 
-func TestCreateIssueAttachment(t *testing.T) {
-	defer tests.PrepareTestEnv(t)()
+func testCreateUser2IssueAttachment(t *testing.T) {
 	const repoURL = "user2/repo1"
 	session := loginUser(t, "user2")
 	uuid := testCreateIssueAttachment(t, session, GetUserCSRFToken(t, session), repoURL, "image.png", testGeneratePngBytes(), http.StatusOK)
@@ -90,8 +120,7 @@ func TestCreateIssueAttachment(t *testing.T) {
 	MakeRequest(t, req, http.StatusOK)
 }
 
-func TestGetAttachment(t *testing.T) {
-	defer tests.PrepareTestEnv(t)()
+func testGetAttachment(t *testing.T) {
 	adminSession := loginUser(t, "user1")
 	user2Session := loginUser(t, "user2")
 	user8Session := loginUser(t, "user8")