config: add configurable content security policy (#18085)

.changelog/18085.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+ui: Added configurable content security policy header
+```

command/agent/http.go

@@ -37,6 +37,7 @@ import (
 	"github.com/hashicorp/nomad/helper/tlsutil"
 	"github.com/hashicorp/nomad/nomad"
 	"github.com/hashicorp/nomad/nomad/structs"
+	"github.com/hashicorp/nomad/nomad/structs/config"
 )
 
 const (
@@ -505,7 +506,7 @@ func (s *HTTPServer) registerHandlers(enableDebug bool) {
 	uiConfigEnabled := agentConfig.UI != nil && agentConfig.UI.Enabled
 
 	if uiEnabled && uiConfigEnabled {
-		s.mux.Handle("/ui/", http.StripPrefix("/ui/", s.handleUI(http.FileServer(&UIAssetWrapper{FileSystem: assetFS()}))))
+		s.mux.Handle("/ui/", http.StripPrefix("/ui/", s.handleUI(agentConfig.UI.ContentSecurityPolicy, http.FileServer(&UIAssetWrapper{FileSystem: assetFS()}))))
 		s.logger.Debug("UI is enabled")
 	} else {
 		// Write the stubHTML
@@ -646,10 +647,10 @@ func (e *codedError) Code() int {
 	return e.code
 }
 
-func (s *HTTPServer) handleUI(h http.Handler) http.Handler {
+func (s *HTTPServer) handleUI(policy *config.ContentSecurityPolicy, h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 		header := w.Header()
-		header.Add("Content-Security-Policy", "default-src 'none'; connect-src *; img-src 'self' data:; script-src 'self'; style-src 'self' 'unsafe-inline'; form-action 'none'; frame-ancestors 'none'")
+		header.Add("Content-Security-Policy", policy.String())
 		h.ServeHTTP(w, req)
 	})
 }

nomad/structs/config/ui.go

@@ -3,6 +3,13 @@
 
 package config
 
+import (
+	"fmt"
+	"strings"
+
+	"golang.org/x/exp/slices"
+)
+
 // UIConfig contains the operator configuration of the web UI
 // Note:
 // before extending this configuration, consider reviewing NMD-125
@@ -11,6 +18,9 @@ type UIConfig struct {
 	// Enabled is used to enable the web UI
 	Enabled bool `hcl:"enabled"`
 
+	// ContentSecurityPolicy is used to configure the CSP header
+	ContentSecurityPolicy *ContentSecurityPolicy `hcl:"content_security_policy"`
+
 	// Consul configures deep links for Consul UI
 	Consul *ConsulUIConfig `hcl:"consul"`
 
@@ -21,6 +31,87 @@ type UIConfig struct {
 	Label *LabelUIConfig `hcl:"label"`
 }
 
+// only covers the elements of
+// https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP we need or care about
+type ContentSecurityPolicy struct {
+	ConnectSrc     []string `hcl:"connect_src"`
+	DefaultSrc     []string `hcl:"default_src"`
+	FormAction     []string `hcl:"form_action"`
+	FrameAncestors []string `hcl:"frame_ancestors"`
+	ImgSrc         []string `hcl:"img_src"`
+	ScriptSrc      []string `hcl:"script_src"`
+	StyleSrc       []string `hcl:"style_src"`
+}
+
+// Copy returns a copy of this Vault UI config.
+func (old *ContentSecurityPolicy) Copy() *ContentSecurityPolicy {
+	if old == nil {
+		return nil
+	}
+
+	nc := new(ContentSecurityPolicy)
+	*nc = *old
+	nc.ConnectSrc = slices.Clone(old.ConnectSrc)
+	nc.DefaultSrc = slices.Clone(old.DefaultSrc)
+	nc.FormAction = slices.Clone(old.FormAction)
+	nc.FrameAncestors = slices.Clone(old.FrameAncestors)
+	nc.ImgSrc = slices.Clone(old.ImgSrc)
+	nc.ScriptSrc = slices.Clone(old.ScriptSrc)
+	nc.StyleSrc = slices.Clone(old.StyleSrc)
+	return nc
+}
+
+func (csp *ContentSecurityPolicy) String() string {
+	return fmt.Sprintf("default-src %s; connect-src %s; img-src %s; script-src %s; style-src %s; form-action %s; frame-ancestors %s", strings.Join(csp.DefaultSrc, " "), strings.Join(csp.ConnectSrc, " "), strings.Join(csp.ImgSrc, " "), strings.Join(csp.ScriptSrc, " "), strings.Join(csp.StyleSrc, " "), strings.Join(csp.FormAction, " "), strings.Join(csp.FrameAncestors, " "))
+}
+
+func (csp *ContentSecurityPolicy) Merge(other *ContentSecurityPolicy) *ContentSecurityPolicy {
+	result := csp.Copy()
+	if result == nil {
+		result = &ContentSecurityPolicy{}
+	}
+	if other == nil {
+		return result
+	}
+
+	if len(other.ConnectSrc) > 0 {
+		result.ConnectSrc = other.ConnectSrc
+	}
+	if len(other.DefaultSrc) > 0 {
+		result.DefaultSrc = other.DefaultSrc
+	}
+	if len(other.FormAction) > 0 {
+		result.FormAction = other.FormAction
+	}
+	if len(other.FrameAncestors) > 0 {
+		result.FrameAncestors = other.FrameAncestors
+	}
+	if len(other.ImgSrc) > 0 {
+		result.ImgSrc = other.ImgSrc
+	}
+	if len(other.ScriptSrc) > 0 {
+		result.ScriptSrc = other.ScriptSrc
+	}
+	if len(other.StyleSrc) > 0 {
+		result.StyleSrc = other.StyleSrc
+	}
+
+	return result
+
+}
+
+func DefaultCSPConfig() *ContentSecurityPolicy {
+	return &ContentSecurityPolicy{
+		ConnectSrc:     []string{"*"},
+		DefaultSrc:     []string{"'none'"},
+		FormAction:     []string{"'none'"},
+		FrameAncestors: []string{"'none'"},
+		ImgSrc:         []string{"'self'", "data:"},
+		ScriptSrc:      []string{"'self'"},
+		StyleSrc:       []string{"'self'", "'unsafe-inline'"},
+	}
+}
+
 // ConsulUIConfig configures deep links to this cluster's Consul
 type ConsulUIConfig struct {
 
@@ -51,6 +142,7 @@ func DefaultUIConfig() *UIConfig {
 		Consul:                &ConsulUIConfig{},
 		Vault:                 &VaultUIConfig{},
 		Label:                 &LabelUIConfig{},
+		ContentSecurityPolicy: DefaultCSPConfig(),
 	}
 }
 
@@ -84,6 +176,7 @@ func (old *UIConfig) Merge(other *UIConfig) *UIConfig {
 	result.Consul = result.Consul.Merge(other.Consul)
 	result.Vault = result.Vault.Merge(other.Vault)
 	result.Label = result.Label.Merge(other.Label)
+	result.ContentSecurityPolicy = result.ContentSecurityPolicy.Merge(other.ContentSecurityPolicy)
 
 	return result
 }

nomad/structs/config/ui_test.go

@@ -26,6 +26,7 @@ func TestUIConfig_Merge(t *testing.T) {
 			BackgroundColor: "blue",
 			TextColor:       "#fff",
 		},
+		ContentSecurityPolicy: DefaultCSPConfig(),
 	}
 
 	testCases := []struct {
@@ -64,6 +65,7 @@ func TestUIConfig_Merge(t *testing.T) {
 				Consul: &ConsulUIConfig{
 					BaseUIURL: "http://consul-other.example.com:8500",
 				},
+				ContentSecurityPolicy: DefaultCSPConfig(),
 			},
 			right: &UIConfig{},
 			expect: &UIConfig{
@@ -73,6 +75,7 @@ func TestUIConfig_Merge(t *testing.T) {
 				},
 				Vault:                 &VaultUIConfig{},
 				Label:                 &LabelUIConfig{},
+				ContentSecurityPolicy: DefaultCSPConfig(),
 			},
 		},
 	}

website/content/docs/configuration/ui.mdx

@@ -16,6 +16,16 @@ The `ui` block configures the Nomad agent's [web UI].
 ui {
   enabled =  true
 
+  content_security_policy {
+    connect_src     = ["*"]
+    default_src     = ["'none'"]
+    form_action     = ["'none'"]
+    frame_ancestors = ["'none'"]
+    img_src         = ["'self'","data:"]
+    script_src      = ["'self'"]
+    style_src       = ["'self'","'unsafe-inline'"]
+  }
+
   consul {
     ui_url = "https://consul.example.com:8501/ui"
   }
@@ -48,6 +58,27 @@ and the configuration is individual to each agent.
 - `label` <code>([Label]: nil)</code> - Configures a user-defined
   label to display in the Nomad Web UI header.
 
+## `content_security_policy` Parameters
+
+The `content_security_policy` block configures the HTTP
+[Content-Security-Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP)
+header sent with the web UI response.
+
+- `connect_src` `(array<string>: ["*"])` - Specifies the valid sources for
+  `connect-src` in the Content Security Policy header.
+- `default_src` `(array<string>: ["'none'"])` - Specifies the valid sources for
+  `default-src` in the Content Security Policy header.
+- `form_action` `(array<string>: ["'none'"])` - Specifies the valid sources for
+  `form-action` in the Content Security Policy header.
+- `frame_ancestors` `(array<string>: ["'none'"])` - Specifies the valid sources
+  for `frame-ancestors` in the Content Security Policy header.
+- `img_src` `(array<string>: ["'self'", "data:"])` - Specifies the valid sources
+  for `img-src` in the Content Security Policy header.
+- `script_src` `(array<string>: ["'self'"])` - Specifies the valid sources for
+  `script-src` in the Content Security Policy header.
+- `style_src` `(array<string>: ["'self'","'unsafe-inline'"])` - Specifies the
+  valid sources for `style-src` in the Content Security Policy header.
+
 ## `consul` Parameters
 
 - `ui_url` `(string: "")` - Specifies the full base URL to a Consul