feat: strip Permissions-Policy and Feature-Policy headers and prevent sync XHR when disallowed by policy

Author: lemon-mint

internal/headers/policy.go

@@ -8,6 +8,7 @@ import (
 var hidden = map[string]struct{}{
 	"set-cookie": {}, "set-cookie2": {},
 	"content-security-policy": {}, "content-security-policy-report-only": {},
+	"permissions-policy": {}, "feature-policy": {},
 	"report-to": {}, "reporting-endpoints": {}, "nel": {},
 	"service-worker-allowed": {},
 	"sourcemap":              {}, "x-sourcemap": {},

internal/headers/policy_freeze_test.go

@@ -18,6 +18,7 @@ func TestConstructorPolicyStripsFullHiddenSet(t *testing.T) {
 	strip := []string{
 		"Set-Cookie", "Set-Cookie2",
 		"Content-Security-Policy", "Content-Security-Policy-Report-Only",
+		"Permissions-Policy", "Feature-Policy",
 		"Report-To", "Reporting-Endpoints", "NEL",
 		"Service-Worker-Allowed",
 		"SourceMap", "X-SourceMap",
@@ -140,7 +141,8 @@ func TestConstructorPolicyStripsLocationAndHopByHop(t *testing.T) {
 func TestHiddenHeaderTableOracle(t *testing.T) {
 	hiddenTrue := []string{
 		"set-cookie", "SET-COOKIE2", "content-security-policy",
-		"content-security-policy-report-only", "report-to", "reporting-endpoints",
+		"content-security-policy-report-only", "permissions-policy", "feature-policy",
+		"report-to", "reporting-endpoints",
 		"nel", "service-worker-allowed", "sourcemap", "x-sourcemap",
 		"alt-svc", "link", "refresh", "clear-site-data",
 		// hop-by-hop

internal/headers/policy_oracle_test.go

@@ -86,6 +86,8 @@ func policyOracleCorpus() []policyOracleCase {
 				// stripped:
 				"Set-Cookie":              {"sid=1; Path=/"},
 				"Content-Security-Policy": {"default-src 'self'"},
+				"Permissions-Policy":      {"sync-xhr=()"},
+				"Feature-Policy":          {"sync-xhr 'none'"},
 				"Location":                {"https://target.example/next"},
 				"Alt-Svc":                 {"h3=\":443\""},
 				"Connection":              {"keep-alive"},

internal/headers/policy_test.go

@@ -6,9 +6,9 @@ import (
 )
 
 func TestConstructorPolicyStripsForbiddenHeaders(t *testing.T) {
-	h := http.Header{"Set-Cookie": {"a=b"}, "Content-Security-Policy": {"default-src *"}, "Location": {"https://target/"}, "Alt-Svc": {"h3=\":443\""}, "Content-Type": {"text/html"}, "Content-Length": {"10"}}
+	h := http.Header{"Set-Cookie": {"a=b"}, "Content-Security-Policy": {"default-src *"}, "Permissions-Policy": {"sync-xhr=()"}, "Location": {"https://target/"}, "Alt-Svc": {"h3=\":443\""}, "Content-Type": {"text/html"}, "Content-Length": {"10"}}
 	out := ConstructorPolicy(h, true, false)
-	for _, name := range []string{"Set-Cookie", "Content-Security-Policy", "Location", "Alt-Svc", "Content-Length"} {
+	for _, name := range []string{"Set-Cookie", "Content-Security-Policy", "Permissions-Policy", "Location", "Alt-Svc", "Content-Length"} {
 		if out.Get(name) != "" {
 			t.Fatalf("%s leaked: %#v", name, out)
 		}

scripts/build.mjs

@@ -242,7 +242,8 @@ async function makeRustRewriterClassic() {
     `let initError = null;`,
     `let initPromise = null;`,
     `function wasmSource() { return WASM_URL; }`,
-    `function loadWasmBytesSync() { if (typeof XMLHttpRequest !== 'function') return null; const xhr = new XMLHttpRequest(); xhr.open('GET', WASM_URL, false); if (xhr.overrideMimeType) xhr.overrideMimeType('text/plain; charset=x-user-defined'); xhr.send(null); if (!((xhr.status >= 200 && xhr.status < 300) || xhr.status === 0)) throw new Error('RUST_REWRITER_WASM_HTTP_' + xhr.status); const text = String(xhr.responseText || ''); const bytes = new Uint8Array(text.length); for (let i = 0; i < text.length; i++) bytes[i] = text.charCodeAt(i) & 255; return bytes; }`,
+    `function syncXHRAllowed() { const doc = globalThis.document; const policy = doc && (doc.permissionsPolicy || doc.featurePolicy); if (!policy || typeof policy.allowsFeature !== 'function') return true; try { return policy.allowsFeature('sync-xhr'); } catch { return true; } }`,
+    `function loadWasmBytesSync() { if (typeof XMLHttpRequest !== 'function' || !syncXHRAllowed()) return null; const xhr = new XMLHttpRequest(); xhr.open('GET', WASM_URL, false); if (xhr.overrideMimeType) xhr.overrideMimeType('text/plain; charset=x-user-defined'); xhr.send(null); if (!((xhr.status >= 200 && xhr.status < 300) || xhr.status === 0)) throw new Error('RUST_REWRITER_WASM_HTTP_' + xhr.status); const text = String(xhr.responseText || ''); const bytes = new Uint8Array(text.length); for (let i = 0; i < text.length; i++) bytes[i] = text.charCodeAt(i) & 255; return bytes; }`,
     `function clearWasmTiming() { try { if (globalThis.performance && typeof globalThis.performance.clearResourceTimings === 'function') globalThis.performance.clearResourceTimings(); } catch {} }`,
     `function init() { if (initialized) return Promise.resolve(true); if (!initPromise) initPromise = wasm_bindgen({ module_or_path: wasmSource() }).then(() => { initialized = true; clearWasmTiming(); return true; }).catch(err => { initError = err; initPromise = null; throw err; }); return initPromise; }`,
     `function initSync(bytes) { const source = bytes || loadWasmBytesSync(); if (!source) return false; if (!initialized) { wasm_bindgen.initSync({ module: source }); initialized = true; clearWasmTiming(); } return true; }`,

test/e2e/expected-deltas.json

@@ -7,6 +7,14 @@
     "policyHeaders.reportOnly": {
       "proxy": "",
       "native": "default-src 'none'; connect-src 'none'"
+    },
+    "policyHeaders.permissionsPolicy": {
+      "proxy": "",
+      "native": "sync-xhr=()"
+    },
+    "policyHeaders.featurePolicy": {
+      "proxy": "",
+      "native": "sync-xhr 'none'"
     }
   },
   "nativeVsZeroProxyRawSetDifferentialAllowlist": [
@@ -20,6 +28,16 @@
       "pattern": "^policyHeaders\\.reportOnly$",
       "reason": "ZeroProxy strips upstream report-only policy before constructing proxy responses."
     },
+    {
+      "id": "membrane-permissions-policy-header",
+      "pattern": "^policyHeaders\\.permissionsPolicy$",
+      "reason": "ZeroProxy strips upstream permissions policy before constructing proxy responses."
+    },
+    {
+      "id": "membrane-feature-policy-header",
+      "pattern": "^policyHeaders\\.featurePolicy$",
+      "reason": "ZeroProxy strips upstream legacy feature policy before constructing proxy responses."
+    },
     {
       "id": "canvas-randomization",
       "pattern": "^surface\\.fingerprint\\.canvas\\.(length|stableRead)$",

test/e2e/proxy.test.js

@@ -753,7 +753,9 @@ function createTargetServer(requests) {
               return {
                 text: await policyHeaders.text(),
                 csp: policyHeaders.headers.get('Content-Security-Policy') || '',
-                reportOnly: policyHeaders.headers.get('Content-Security-Policy-Report-Only') || ''
+                reportOnly: policyHeaders.headers.get('Content-Security-Policy-Report-Only') || '',
+                permissionsPolicy: policyHeaders.headers.get('Permissions-Policy') || '',
+                featurePolicy: policyHeaders.headers.get('Feature-Policy') || ''
               };
             })(), 'policy-headers');
             const redirected = await fetch('/redirect302?diff=1', { cache: 'no-store' });
@@ -1109,6 +1111,8 @@ function createTargetServer(requests) {
         'Cache-Control': 'no-store',
         'Content-Security-Policy': "default-src 'none'; script-src 'none'",
         'Content-Security-Policy-Report-Only': "default-src 'none'; connect-src 'none'",
+        'Permissions-Policy': 'sync-xhr=()',
+        'Feature-Policy': "sync-xhr 'none'",
       });
       res.end('policy-header-ok');
       return;

test/js/static-policy.test.js

@@ -350,11 +350,25 @@ test('runtime HTTP facade resolves relative requests without site-specific host
 
 test('Rust rewriter bootstrap falls back to async WASM load if sync bytes fail', () => {
   const build = fs.readFileSync('scripts/build.mjs', 'utf8');
+  assert.ok(build.includes("policy.allowsFeature('sync-xhr')"));
+  assert.ok(build.includes("typeof XMLHttpRequest !== 'function' || !syncXHRAllowed()"));
   assert.ok(build.includes('function bootstrapInit()'));
   assert.ok(build.includes('try { if (initSync()) return; } catch {} init().catch(() => {})'));
   assert.ok(build.includes('bootstrapInit();'));
 });
 
+test('response wrappers strip target permissions policy headers', () => {
+  const swResponses = fs.readFileSync('web/sw/responses.js', 'utf8');
+  assert.ok(swResponses.includes("h.delete('Permissions-Policy')"));
+  assert.ok(swResponses.includes("h.delete('Feature-Policy')"));
+});
+
+test('runtime sync XHR avoids native sync requests when policy disables them', () => {
+  const rt = readRuntimeSource();
+  assert.ok(rt.includes("policy.allowsFeature('sync-xhr')"));
+  assert.ok(rt.includes('if (!syncXHRAllowed()) return failSyncXHR(xhr);'));
+});
+
 test('HTML document transform is a thin Go wrapper over Rust lol_html policy', () => {
   const htmltx = fs.readFileSync('internal/htmltx/transform.go', 'utf8');
   const kernel = fs.readFileSync('cmd/wasm-kernel/main.go', 'utf8');

web/runtime-prelude.mjs

@@ -1448,11 +1448,24 @@ import { createWorkerFacades } from './runtime/workers/facades.mjs';
         if (xhr.readyState !== UNSENT && xhr.readyState !== OPENED || xhr._sent) throw normalizedError('InvalidStateError');
         xhr._withCredentials = !!value;
       }
+      function syncXHRAllowed() {
+        const doc = root.document;
+        const policy = doc && (doc.permissionsPolicy || doc.featurePolicy);
+        if (!policy || typeof policy.allowsFeature !== 'function') return true;
+        try { return policy.allowsFeature('sync-xhr'); } catch { return true; }
+      }
+      function failSyncXHR(xhr) {
+        xhr.status = 0;
+        xhr.statusText = '';
+        xhr._sent = false;
+        xhrDone(xhr, 'error');
+      }
       function sendSyncXHR(xhr, body) {
         if (xhr._timeout) throw normalizedError('InvalidAccessError');
         if (xhr._responseType && xhr._responseType !== 'text') throw normalizedError('InvalidAccessError');
         xhr._sent = true;
         fireEvent(xhr, 'loadstart');
+        if (!syncXHRAllowed()) return failSyncXHR(xhr);
         const nativeXHR = new Native.XMLHttpRequest();
         const internal = isZeroProxyAssetURL(xhr._url);
         nativeXHR.open(xhr._method, internal ? xhr._url : `${ZP.apiPath('fetch')}?url=${encodeURIComponent(xhr._url)}`, false);
@@ -1484,12 +1497,7 @@ import { createWorkerFacades } from './runtime/workers/facades.mjs';
           if (xhr._responseType === 'document') xhr.response = xhr.responseXML;
           xhr._sent = false;
           xhrDone(xhr, 'load');
-        } catch {
-          xhr.status = 0;
-          xhr.statusText = '';
-          xhr._sent = false;
-          xhrDone(xhr, 'error');
-        }
+        } catch { failSyncXHR(xhr); }
       }
       Object.defineProperties(ZPXMLHttpRequest.prototype, {
         [Symbol.toStringTag]: { value: 'XMLHttpRequest', configurable: true },

web/sw/responses.js

@@ -85,6 +85,8 @@
     const h = new Headers(resp.headers);
     const allowDynamicCompile = h.get('X-ZP-Dynamic-Compile') === '1';
     h.delete('X-ZP-Dynamic-Compile');
+    h.delete('Permissions-Policy');
+    h.delete('Feature-Policy');
     h.set('Content-Security-Policy', ZP.fixedCSP(servers || [], { allowDynamicCompile }));
     h.set('X-Content-Type-Options', 'nosniff');
     h.set('Cache-Control', h.get('Cache-Control') || 'no-store');