diff --git a/embed.html b/embed.html
index eefea746..14464d7c 100644
--- a/embed.html
+++ b/embed.html
@@ -2,6 +2,17 @@
 <html lang="en">
   <head>
     <meta charset="UTF-8" />
+    <!--
+      Content-Security-Policy for the embeddable player. Same strict script-src
+      as index.html (same inline theme-bootstrap hash). frame-ancestors is left
+      unset on purpose: this page is meant to be embedded anywhere. If you
+      change the inline theme script below, update the sha256 hash here
+      (tests/csp-policy.test.mjs enforces this).
+    -->
+    <meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'self'; script-src 'self' 'sha256-dnv/l3q8gLqdw0etekr5/atoIRbM/wSVSgQjZEsC7G0=' https://cdn.jsdelivr.net https://esm.sh; style-src 'self' 'unsafe-inline'; img-src 'self' https: data: blob:; media-src 'self' https: blob: mediastream:; connect-src 'self' https: wss: blob: data:; worker-src 'self' blob:; font-src 'self' data:; frame-src 'self'; object-src 'none'; base-uri 'self'; form-action 'self'; manifest-src 'self'"
+    />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>bitvid | Embed</title>
 
diff --git a/index.html b/index.html
index 7672fb65..b392f603 100644
--- a/index.html
+++ b/index.html
@@ -2,6 +2,25 @@
 <html lang="en">
   <head>
     <meta charset="UTF-8" />
+    <!--
+      Content-Security-Policy: defense-in-depth against XSS. The critical
+      directive is script-src, which is strict — only same-origin scripts, the
+      hash of the inline theme-bootstrap below, and the nostr-tools CDN
+      fallbacks (js/nostrToolsBootstrap.js). No 'unsafe-inline'/'unsafe-eval'
+      (verified: no bundle uses eval/Function/wasm). This blocks injected
+      script and object elements, inline handlers (none exist), and base-tag
+      hijack, so an injected payload cannot execute and read the in-memory
+      storage master key / signer / DM plaintext. connect/img/media stay broad
+      because relays, R2/S3 endpoints, and video/thumbnail URLs are
+      user/content defined. If you change the inline theme script below, update
+      the sha256 hash here (tests/csp-policy.test.mjs enforces this).
+      NOTE: any future view loaded by js/viewManager.js must use external-src
+      script tags (script-src 'self'), not inline scripts.
+    -->
+    <meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'self'; script-src 'self' 'sha256-dnv/l3q8gLqdw0etekr5/atoIRbM/wSVSgQjZEsC7G0=' https://cdn.jsdelivr.net https://esm.sh; style-src 'self' 'unsafe-inline'; img-src 'self' https: data: blob:; media-src 'self' https: blob: mediastream:; connect-src 'self' https: wss: blob: data:; worker-src 'self' blob:; font-src 'self' data:; frame-src 'self'; object-src 'none'; base-uri 'self'; form-action 'self'; manifest-src 'self'"
+    />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>bitvid | Decentralized Video Sharing</title>
 
diff --git a/tests/csp-policy.test.mjs b/tests/csp-policy.test.mjs
new file mode 100644
index 00000000..6f3e1bea
--- /dev/null
+++ b/tests/csp-policy.test.mjs
@@ -0,0 +1,103 @@
+// Regression test for the Content-Security-Policy on the HTML entry points.
+//
+// SCN-csp-script-src-locks-inline-hash:
+//   Given index.html / embed.html ship a CSP whose security depends on a strict
+//     script-src (no 'unsafe-inline'),
+//   When the inline bootstrap <script> is hashed,
+//   Then that exact sha256 must be listed in script-src — otherwise the browser
+//     blocks our own bootstrap (app broken) or someone added 'unsafe-inline'
+//     (XSS protection silently gutted).
+//
+// This catches the most likely future regression: editing the inline script
+// without updating the hash, or relaxing script-src to make it "work".
+
+import { readFileSync } from "node:fs";
+import { createHash } from "node:crypto";
+import { fileURLToPath } from "node:url";
+import path from "node:path";
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+
+function extractCsp(html) {
+  // The content value itself contains single quotes ('self', 'none', hashes),
+  // so capture up to the same quote char that opens the attribute.
+  const meta = html.match(
+    /<meta\s+http-equiv=["']Content-Security-Policy["']\s+content=(["'])([\s\S]*?)\1/i,
+  );
+  return meta ? meta[2] : "";
+}
+
+function parseDirectives(csp) {
+  const map = new Map();
+  for (const part of csp.split(";")) {
+    const trimmed = part.trim();
+    if (!trimmed) continue;
+    const [name, ...values] = trimmed.split(/\s+/);
+    map.set(name.toLowerCase(), values);
+  }
+  return map;
+}
+
+function inlineScriptHashes(htmlRaw) {
+  // Browsers ignore content inside HTML comments; strip them so prose mentioning
+  // "script" in a comment is not mistaken for a real inline <script>.
+  const html = htmlRaw.replace(/<!--[\s\S]*?-->/g, "");
+  const re = /<script(?![^>]*\bsrc=)[^>]*>([\s\S]*?)<\/script>/gi;
+  const hashes = [];
+  let m;
+  while ((m = re.exec(html))) {
+    hashes.push(
+      "sha256-" + createHash("sha256").update(m[1], "utf8").digest("base64"),
+    );
+  }
+  return hashes;
+}
+
+for (const file of ["index.html", "embed.html"]) {
+  test(`${file}: CSP exists and script-src is strict`, () => {
+    const html = readFileSync(path.join(ROOT, file), "utf8");
+    const csp = extractCsp(html);
+    assert.ok(csp, `${file} must declare a Content-Security-Policy meta`);
+
+    const directives = parseDirectives(csp);
+    const scriptSrc = directives.get("script-src");
+    assert.ok(scriptSrc, "script-src must be set");
+
+    // The whole point: script execution must NOT be wide open.
+    assert.ok(
+      !scriptSrc.includes("'unsafe-inline'"),
+      "script-src must not allow 'unsafe-inline' (defeats XSS protection)",
+    );
+    assert.ok(
+      !scriptSrc.includes("'unsafe-eval'"),
+      "script-src must not allow 'unsafe-eval' (no bundle needs it)",
+    );
+    assert.ok(scriptSrc.includes("'self'"), "script-src must include 'self'");
+
+    // object-src/base-uri are cheap, high-value XSS hardening.
+    assert.deepEqual(
+      directives.get("object-src"),
+      ["'none'"],
+      "object-src must be 'none'",
+    );
+    assert.deepEqual(
+      directives.get("base-uri"),
+      ["'self'"],
+      "base-uri must be 'self'",
+    );
+  });
+
+  test(`${file}: every inline <script> is hash-allowlisted in script-src`, () => {
+    const html = readFileSync(path.join(ROOT, file), "utf8");
+    const scriptSrc = parseDirectives(extractCsp(html)).get("script-src") || [];
+    for (const hash of inlineScriptHashes(html)) {
+      assert.ok(
+        scriptSrc.includes(`'${hash}'`),
+        `inline <script> in ${file} has hash ${hash} which is not listed in ` +
+          `script-src — update the CSP meta after editing the inline script`,
+      );
+    }
+  });
+}