diff --git a/package.json b/package.json
index 0a1df880..6d8826d8 100644
--- a/package.json
+++ b/package.json
@@ -22,6 +22,7 @@
     "file-loader": "^6.2.0",
     "fs-extra": "^9.0.1",
     "html-webpack-plugin": "^4.5.0",
+    "jsdom": "^29.1.1",
     "json-loader": "^0.5.7",
     "jstrace": "^0.3.0",
     "less": "^3.13.1",
@@ -30,6 +31,7 @@
     "run-all": "^1.0.1",
     "run-s": "0.0.0",
     "style-loader": "^2.0.0",
+    "terser-webpack-plugin": "^5.6.1",
     "trash": "^7.1.0",
     "webpack": "^5.11.0",
     "webpack-cli": "^4.7.0",
@@ -40,7 +42,7 @@
     "start": "webpack serve --config webpack.dev.js --open",
     "build": "webpack --config webpack.prd.js && node tasks/compile_less.js",
     "clean": "trash dist",
-    "test": "echo \"Error: no test specified\" && exit 1",
+    "test": "node --test \"tests/js/**/*.test.mjs\"",
     "dist": "npm-run-all -s clean build && cp dist/js/storymap.js dist/js/storymap-min.js",
     "stage": "npm run dist && node tasks/stage.js",
     "stage_latest": "npm run dist && node tasks/stage.js latest",
diff --git a/src/js/media/EmbedUtil.js b/src/js/media/EmbedUtil.js
new file mode 100644
index 00000000..2c7ffba0
--- /dev/null
+++ b/src/js/media/EmbedUtil.js
@@ -0,0 +1,118 @@
+/*	EmbedUtil
+	Utilities for safely rendering user-pasted embed snippets.
+
+	The media "url" field is overloaded: for the iframe and blockquote
+	media types it holds raw HTML pasted by the user (that markup is
+	what routes the media to those types in MediaType.js). These helpers
+	parse that HTML inertly -- DOMParser never executes scripts or event
+	handlers -- and rebuild clean DOM from an allowlist, so markup stored
+	in a storymap's JSON can never execute code in a viewer's browser.
+================================================== */
+
+// Attributes copied from a pasted <iframe> onto the rebuilt element.
+// src is handled separately (validated); everything else is dropped.
+const IFRAME_ATTRIBUTES = ["width", "height", "frameborder", "allowfullscreen", "allow", "scrolling", "title"];
+
+// Tags allowed to survive blockquote sanitization. Elements not listed
+// are unwrapped (their children are kept); DROP_TAGS are removed along
+// with their contents.
+const BLOCKQUOTE_TAGS = ["BLOCKQUOTE", "P", "CITE", "EM", "STRONG", "B", "I", "U", "Q", "A", "BR", "SPAN", "SMALL", "SUP", "SUB", "FOOTER", "UL", "OL", "LI"];
+const DROP_TAGS = ["SCRIPT", "STYLE", "TEMPLATE", "IFRAME", "FRAME", "OBJECT", "EMBED", "APPLET", "LINK", "META", "BASE", "SVG", "MATH", "FORM", "INPUT", "BUTTON", "TEXTAREA", "SELECT"];
+
+function parseInert(html) {
+	return new DOMParser().parseFromString(html, "text/html");
+}
+
+/*	Return an absolute http(s) URL for url, or null if it is empty,
+	unparseable, or uses any other protocol (javascript:, data:, ...).
+	Relative and protocol-relative URLs resolve against the document.
+================================================== */
+export function validateWebURL(url) {
+	if (!url) {
+		return null;
+	}
+	var a = document.createElement("a");
+	a.href = url;
+	if (a.protocol === "http:" || a.protocol === "https:") {
+		return a.href;
+	}
+	return null;
+}
+
+/*	Build a clean <iframe> element from a pasted embed snippet.
+	Only the validated src and allowlisted presentation attributes
+	survive; event handlers, extra tags and scripts are discarded.
+	Also accepts a bare URL for the src. Returns null if no safe
+	src can be extracted.
+================================================== */
+export function buildIframe(html) {
+	var pasted = parseInert(html).querySelector("iframe");
+	var src = null;
+
+	if (pasted) {
+		src = validateWebURL(pasted.getAttribute("src"));
+	} else if (/^https?:\/\/\S+$/i.test(html.trim())) {
+		// The field held a bare URL rather than an embed snippet
+		src = validateWebURL(html.trim());
+	}
+	if (!src) {
+		return null;
+	}
+
+	var iframe = document.createElement("iframe");
+	iframe.setAttribute("src", src);
+	if (pasted) {
+		for (var i = 0; i < IFRAME_ATTRIBUTES.length; i++) {
+			if (pasted.hasAttribute(IFRAME_ATTRIBUTES[i])) {
+				iframe.setAttribute(IFRAME_ATTRIBUTES[i], pasted.getAttribute(IFRAME_ATTRIBUTES[i]));
+			}
+		}
+	} else {
+		iframe.setAttribute("width", "100%");
+		iframe.setAttribute("height", "100%");
+		iframe.setAttribute("frameborder", "0");
+		iframe.setAttribute("allowfullscreen", "");
+	}
+	return iframe;
+}
+
+/*	Sanitize pasted blockquote markup into a DocumentFragment.
+	Allowlisted formatting tags are kept (with all attributes stripped,
+	except a validated href on links), unknown tags are unwrapped, and
+	executable/embedding tags are dropped with their contents.
+================================================== */
+export function sanitizeBlockquote(html) {
+	var fragment = document.createDocumentFragment();
+	appendSanitized(parseInert(html).body, fragment);
+	return fragment;
+}
+
+function appendSanitized(node, parent) {
+	for (var i = 0; i < node.childNodes.length; i++) {
+		var child = node.childNodes[i];
+		if (child.nodeType === 3) {
+			parent.appendChild(document.createTextNode(child.nodeValue));
+		} else if (child.nodeType === 1) {
+			var tag = child.nodeName.toUpperCase();
+			if (DROP_TAGS.indexOf(tag) !== -1) {
+				continue;
+			}
+			if (BLOCKQUOTE_TAGS.indexOf(tag) !== -1) {
+				var el = document.createElement(tag);
+				if (tag === "A") {
+					var href = validateWebURL(child.getAttribute("href"));
+					if (href) {
+						el.setAttribute("href", href);
+						el.setAttribute("target", "_blank");
+					}
+				}
+				appendSanitized(child, el);
+				parent.appendChild(el);
+			} else {
+				// Unknown tag: unwrap, keeping its children
+				appendSanitized(child, parent);
+			}
+		}
+		// Comments and other node types are dropped
+	}
+}
diff --git a/src/js/media/types/Blockquote.js b/src/js/media/types/Blockquote.js
index 4ad799d9..396cf5f0 100644
--- a/src/js/media/types/Blockquote.js
+++ b/src/js/media/types/Blockquote.js
@@ -1,29 +1,32 @@
 import { Media } from "../Media"
 import Dom from "../../dom/Dom"
-import { Language } from "../../language/Language"                              
+import { Language } from "../../language/Language"
+import { sanitizeBlockquote } from "../EmbedUtil"
 
 
 /*	Media.Blockquote
 ================================================== */
 
 export default class Blockquote extends Media {
-	
+
 	/*	Load the media
 	================================================== */
 	_loadMedia() {
-		
+
 		// Loading Message
 		this.message.updateMessage(Language.messages.loading + " " + this.options.media_name);
-		
+
 		// Create Dom element
 		this._el.content_item	= Dom.create("div", "vco-media-item vco-media-blockquote", this._el.content);
-		
+
 		// Get Media ID
 		this.media_id = this.data.url;
-		
-		// API Call
-		this._el.content_item.innerHTML = this.media_id;
-		
+
+		// The url field holds user-pasted blockquote markup. Sanitize it
+		// instead of injecting the raw markup, which would allow stored
+		// XSS via the storymap JSON.
+		this._el.content_item.appendChild(sanitizeBlockquote(this.media_id));
+
 		// After Loaded
 		this.onLoaded();
 	}
diff --git a/src/js/media/types/IFrame.js b/src/js/media/types/IFrame.js
index ebb1e714..d9025d2c 100644
--- a/src/js/media/types/IFrame.js
+++ b/src/js/media/types/IFrame.js
@@ -1,32 +1,40 @@
 import { Media } from "../Media"
 import Dom from "../../dom/Dom"
-import { Language } from "../../language/Language"                              
+import { Language } from "../../language/Language"
+import { buildIframe } from "../EmbedUtil"
 
 /*	Media.IFrame
 ================================================== */
 
 export default class IFrame extends Media {
-	
+
 	/*	Load the media
 	================================================== */
 	_loadMedia() {
 		self = this;
-		
+
 		// Loading Message
 		this.message.updateMessage(Language.messages.loading + " " + this.options.media_name);
-		
+
 		// Create Dom element
 		this._el.content_item	= Dom.create("div", "vco-media-item vco-media-iframe", this._el.content);
-		
+
 		// Get Media ID
 		this.media_id = this.data.url;
-		
-		// API URL
-		let iframe = this.media_id;
+
+		// The url field holds a user-pasted embed snippet. Rebuild a
+		// clean iframe from its src instead of injecting the raw markup,
+		// which would allow stored XSS via the storymap JSON.
+		let iframe = buildIframe(this.media_id);
+
+		if (!iframe) {
+			this.loadErrorDisplay("Invalid embed code. Paste an iframe embed code with an http(s) source URL.");
+			return;
+		}
 
 		// API Call
-		this._el.content_item.innerHTML = iframe;
-		
+		this._el.content_item.appendChild(iframe);
+
 		// After Loaded
 		this.onLoaded();
 	}
diff --git a/tests/js/embed_util.test.mjs b/tests/js/embed_util.test.mjs
new file mode 100644
index 00000000..c7016fcf
--- /dev/null
+++ b/tests/js/embed_util.test.mjs
@@ -0,0 +1,148 @@
+/*	Tests for src/js/media/EmbedUtil.js
+	Run with: npm test (node --test, jsdom provides the DOM)
+================================================== */
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { JSDOM } from "jsdom";
+
+const dom = new JSDOM("<!doctype html><html><body></body></html>", {
+	url: "https://storymap.knightlab.com/edit/",
+});
+global.window = dom.window;
+global.document = dom.window.document;
+global.DOMParser = dom.window.DOMParser;
+
+const { buildIframe, sanitizeBlockquote, validateWebURL } = await import(
+	"../../src/js/media/EmbedUtil.js"
+);
+
+/*	validateWebURL
+================================================== */
+
+test("validateWebURL accepts http and https", () => {
+	assert.equal(validateWebURL("https://example.com/a"), "https://example.com/a");
+	assert.equal(validateWebURL("http://example.com/a"), "http://example.com/a");
+});
+
+test("validateWebURL resolves relative and protocol-relative URLs", () => {
+	assert.equal(validateWebURL("/foo"), "https://storymap.knightlab.com/foo");
+	assert.equal(validateWebURL("//example.com/x"), "https://example.com/x");
+});
+
+test("validateWebURL rejects non-web protocols and empty values", () => {
+	assert.equal(validateWebURL("javascript:alert(1)"), null);
+	assert.equal(validateWebURL("data:text/html,<script>alert(1)</script>"), null);
+	assert.equal(validateWebURL("vbscript:x"), null);
+	assert.equal(validateWebURL(""), null);
+	assert.equal(validateWebURL(null), null);
+});
+
+/*	buildIframe
+================================================== */
+
+test("buildIframe extracts src and presentation attributes from an embed code", () => {
+	const iframe = buildIframe(
+		'<iframe src="https://www.youtube.com/embed/abc123" width="560" height="315" frameborder="0" allowfullscreen></iframe>'
+	);
+	assert.ok(iframe);
+	assert.equal(iframe.tagName, "IFRAME");
+	assert.equal(iframe.getAttribute("src"), "https://www.youtube.com/embed/abc123");
+	assert.equal(iframe.getAttribute("width"), "560");
+	assert.equal(iframe.getAttribute("height"), "315");
+	assert.equal(iframe.getAttribute("frameborder"), "0");
+	assert.ok(iframe.hasAttribute("allowfullscreen"));
+});
+
+test("buildIframe strips event handlers and unknown attributes", () => {
+	const iframe = buildIframe(
+		'<iframe src="https://example.com/" onload="alert(1)" name="evil" srcdoc="<script>alert(1)</script>"></iframe>'
+	);
+	assert.ok(iframe);
+	assert.equal(iframe.getAttribute("onload"), null);
+	assert.equal(iframe.getAttribute("name"), null);
+	assert.equal(iframe.getAttribute("srcdoc"), null);
+});
+
+test("buildIframe discards markup outside the iframe", () => {
+	const iframe = buildIframe(
+		'<img src=x onerror="alert(1)"><iframe src="https://example.com/"></iframe><script>alert(1)</script>'
+	);
+	assert.ok(iframe);
+	assert.equal(iframe.tagName, "IFRAME");
+	assert.equal(iframe.getAttribute("src"), "https://example.com/");
+});
+
+test("buildIframe rejects javascript: src", () => {
+	assert.equal(buildIframe('<iframe src="javascript:alert(1)"></iframe>'), null);
+});
+
+test("buildIframe rejects an iframe with no src", () => {
+	assert.equal(buildIframe("<iframe></iframe>"), null);
+});
+
+test("buildIframe accepts a bare URL that routed to the iframe type", () => {
+	const iframe = buildIframe("https://example.com/iframe-demo");
+	assert.ok(iframe);
+	assert.equal(iframe.getAttribute("src"), "https://example.com/iframe-demo");
+	assert.equal(iframe.getAttribute("width"), "100%");
+});
+
+test("buildIframe returns null for text that is neither embed nor URL", () => {
+	assert.equal(buildIframe("this mentions iframe but embeds nothing"), null);
+});
+
+/*	sanitizeBlockquote
+================================================== */
+
+function renderedHTML(fragment) {
+	const div = document.createElement("div");
+	div.appendChild(fragment);
+	return div.innerHTML;
+}
+
+test("sanitizeBlockquote keeps quote structure and text", () => {
+	const html = renderedHTML(
+		sanitizeBlockquote("<blockquote><p>Truth is <em>rarely</em> pure.</p><cite>Oscar Wilde</cite></blockquote>")
+	);
+	assert.equal(html, "<blockquote><p>Truth is <em>rarely</em> pure.</p><cite>Oscar Wilde</cite></blockquote>");
+});
+
+test("sanitizeBlockquote drops script tags and their contents", () => {
+	const html = renderedHTML(
+		sanitizeBlockquote("<blockquote>quote</blockquote><script>alert(1)</script>")
+	);
+	assert.equal(html, "<blockquote>quote</blockquote>");
+});
+
+test("sanitizeBlockquote strips event handler and style attributes", () => {
+	const html = renderedHTML(
+		sanitizeBlockquote('<blockquote onclick="alert(1)" style="color:red">quote</blockquote>')
+	);
+	assert.equal(html, "<blockquote>quote</blockquote>");
+});
+
+test("sanitizeBlockquote unwraps unknown tags but keeps their text", () => {
+	const html = renderedHTML(
+		sanitizeBlockquote("<div><blockquote>quote</blockquote><h1>heading</h1></div>")
+	);
+	assert.equal(html, "<blockquote>quote</blockquote>heading");
+});
+
+test("sanitizeBlockquote drops img-based XSS entirely", () => {
+	const html = renderedHTML(
+		sanitizeBlockquote('<blockquote>q<img src=x onerror="alert(1)"></blockquote>')
+	);
+	assert.equal(html, "<blockquote>q</blockquote>");
+});
+
+test("sanitizeBlockquote keeps links with valid href, drops javascript: href", () => {
+	const good = renderedHTML(
+		sanitizeBlockquote('<blockquote><a href="https://example.com/">link</a></blockquote>')
+	);
+	assert.equal(good, '<blockquote><a href="https://example.com/" target="_blank">link</a></blockquote>');
+
+	const bad = renderedHTML(
+		sanitizeBlockquote('<blockquote><a href="javascript:alert(1)">link</a></blockquote>')
+	);
+	assert.equal(bad, "<blockquote><a>link</a></blockquote>");
+});