fix: csp regressions (#38047)

fix #37257 , all details are in the comments

modules/setting/markup.go

@@ -237,6 +237,10 @@ func fileExtensionsToPatterns(sectionName string, extensions []string) []string
 	return patterns
 }
 
+// MarkupRenderDefaultSandbox only contains a safe set of "sandbox allow" values, it is used to protect users from XSS attack,
+// DO NOT USE "allow-same-origin" by default: if there is XSS in rendered content, same-origin makes the frame page can access parent window and send requests with user's credentials.
+const MarkupRenderDefaultSandbox = "allow-scripts allow-forms allow-modals allow-popups allow-downloads"
+
 func newMarkupRenderer(name string, sec ConfigSection) {
 	if !sec.Key("ENABLED").MustBool(false) {
 		return
@@ -269,9 +273,7 @@ func newMarkupRenderer(name string, sec ConfigSection) {
 		renderContentMode = RenderContentModeSanitized
 	}
 
-	// ATTENTION! at the moment, only a safe set like "allow-scripts" are allowed for sandbox mode.
-	// "allow-same-origin" should NEVER be used, it leads to XSS attack: makes the JS in iframe can access parent window's config and send requests with user's credentials.
-	renderContentSandbox := sec.Key("RENDER_CONTENT_SANDBOX").MustString("allow-scripts allow-popups")
+	renderContentSandbox := sec.Key("RENDER_CONTENT_SANDBOX").MustString(MarkupRenderDefaultSandbox)
 	if renderContentSandbox == "disabled" {
 		renderContentSandbox = ""
 	}

modules/setting/security.go

@@ -18,6 +18,8 @@ var Security = struct {
 	// TODO: move more settings to this struct in future
 	XFrameOptions       string
 	XContentTypeOptions string
+
+	ContentSecurityPolicyGeneral string // it only supports empty (default policy) or "unset", maybe it can support more in the future
 }{
 	XFrameOptions:       "SAMEORIGIN",
 	XContentTypeOptions: "nosniff",
@@ -150,13 +152,12 @@ func loadSecurityFrom(rootCfg ConfigProvider) {
 	SuccessfulTokensCacheSize = sec.Key("SUCCESSFUL_TOKENS_CACHE_SIZE").MustInt(20)
 
 	deprecatedSetting(rootCfg, "cors", "X_FRAME_OPTIONS", "security", "X_FRAME_OPTIONS", "v1.26.0")
-	if sec.HasKey("X_FRAME_OPTIONS") {
-		Security.XFrameOptions = sec.Key("X_FRAME_OPTIONS").MustString(Security.XFrameOptions)
-	} else {
+	if !sec.HasKey("X_FRAME_OPTIONS") {
 		Security.XFrameOptions = rootCfg.Section("cors").Key("X_FRAME_OPTIONS").MustString(Security.XFrameOptions)
 	}
-
-	Security.XContentTypeOptions = sec.Key("X_CONTENT_TYPE_OPTIONS").MustString(Security.XContentTypeOptions)
+	if err := sec.MapTo(&Security); err != nil {
+		log.Fatal("Failed to map security settings: %v", err)
+	}
 
 	twoFactorAuth := sec.Key("TWO_FACTOR_AUTH").String()
 	switch twoFactorAuth {

modules/setting/security_test.go

@@ -0,0 +1,22 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLoadSecurityFrom(t *testing.T) {
+	cfg, err := NewConfigProviderFromData(`[security]
+X_FRAME_OPTIONS = DENY
+X_CONTENT_TYPE_OPTIONS = unset
+CONTENT_SECURITY_POLICY_GENERAL = "script-src *; foo"`)
+	assert.NoError(t, err)
+	loadSecurityFrom(cfg)
+	assert.Equal(t, "DENY", Security.XFrameOptions)
+	assert.Equal(t, "unset", Security.XContentTypeOptions)
+	assert.Equal(t, `"script-src *`, Security.ContentSecurityPolicyGeneral) // holy shit ini package bug
+}