diff --git a/packages/app-desktop/gui/ShareNoteDialog.tsx b/packages/app-desktop/gui/ShareNoteDialog.tsx
index f5dffc743e..7c6c4aa38a 100644
--- a/packages/app-desktop/gui/ShareNoteDialog.tsx
+++ b/packages/app-desktop/gui/ShareNoteDialog.tsx
@@ -95,7 +95,7 @@ export function ShareNoteDialog(props: Props) {
 
 	const copyLinksToClipboard = (shares: StateShare[]) => {
 		const links = [];
-		for (const share of shares) links.push(ShareService.instance().shareUrl(share));
+		for (const share of shares) links.push(ShareService.instance().shareUrl(ShareService.instance().userId, share));
 		clipboard.writeText(links.join('\n'));
 	};
 
diff --git a/packages/app-desktop/runForSharing.sh b/packages/app-desktop/runForSharing.sh
index ec10c74e5c..6ea7f7a5a2 100755
--- a/packages/app-desktop/runForSharing.sh
+++ b/packages/app-desktop/runForSharing.sh
@@ -25,13 +25,13 @@ if [ "$RESET_ALL" == "1" ]; then
 	rm -rf "$PROFILE_DIR"
 
 	echo "config keychain.supported 0" >> "$CMD_FILE" 
-	echo "config sync.target 9" >> "$CMD_FILE" 
-	echo "config sync.9.path http://api-joplincloud.local:22300" >> "$CMD_FILE" 
-	echo "config sync.9.username $USER_EMAIL" >> "$CMD_FILE" 
-	echo "config sync.9.password 123456" >> "$CMD_FILE" 
+	echo "config sync.target 10" >> "$CMD_FILE" 
+	echo "config sync.10.path http://api.joplincloud.local:22300" >> "$CMD_FILE" 
+	echo "config sync.10.username $USER_EMAIL" >> "$CMD_FILE" 
+	echo "config sync.10.password 123456" >> "$CMD_FILE" 
 
 	if [ "$USER_NUM" == "1" ]; then
-		curl --data '{"action": "createTestUsers"}' -H 'Content-Type: application/json' http://api-joplincloud.local:22300/api/debug
+		curl --data '{"action": "createTestUsers"}' -H 'Content-Type: application/json' http://api.joplincloud.local:22300/api/debug
 
 		echo 'mkbook "shared"' >> "$CMD_FILE"
 		echo 'mkbook "other"' >> "$CMD_FILE"
diff --git a/packages/lib/BaseApplication.ts b/packages/lib/BaseApplication.ts
index 9e517ff750..4247413d5e 100644
--- a/packages/lib/BaseApplication.ts
+++ b/packages/lib/BaseApplication.ts
@@ -768,7 +768,7 @@ export default class BaseApplication {
 		if (Setting.value('env') === Env.Dev) {
 			Setting.setValue('sync.10.path', 'https://api.joplincloud.com');
 			Setting.setValue('sync.10.userContentPath', 'https://joplinusercontent.com');
-			// Setting.setValue('sync.10.path', 'http://api-joplincloud.local:22300');
+			// Setting.setValue('sync.10.path', 'http://api.joplincloud.local:22300');
 			// Setting.setValue('sync.10.userContentPath', 'http://joplinusercontent.local:22300');
 		}
 
diff --git a/packages/lib/JoplinServerApi.ts b/packages/lib/JoplinServerApi.ts
index 7df852fb23..334b36e2cb 100644
--- a/packages/lib/JoplinServerApi.ts
+++ b/packages/lib/JoplinServerApi.ts
@@ -56,8 +56,14 @@ export default class JoplinServerApi {
 		return rtrimSlashes(this.options_.baseUrl());
 	}
 
-	public userContentBaseUrl() {
-		return this.options_.userContentBaseUrl() || this.baseUrl();
+	public userContentBaseUrl(userId: string) {
+		if (this.options_.userContentBaseUrl()) {
+			if (!userId) throw new Error('User ID must be specified');
+			const url = new URL(this.options_.userContentBaseUrl());
+			return `${url.protocol}//${userId.substr(0, 10).toLowerCase()}.${url.host}`;
+		} else {
+			return this.baseUrl();
+		}
 	}
 
 	private async session() {
diff --git a/packages/lib/services/share/ShareService.ts b/packages/lib/services/share/ShareService.ts
index c4f8aeb1ee..2c48cef8b5 100644
--- a/packages/lib/services/share/ShareService.ts
+++ b/packages/lib/services/share/ShareService.ts
@@ -33,6 +33,10 @@ export default class ShareService {
 		return this.store.getState()[stateRootKey] as State;
 	}
 
+	public get userId(): string {
+		return this.api() ? this.api().userId : '';
+	}
+
 	private api(): JoplinServerApi {
 		if (this.api_) return this.api_;
 
@@ -136,8 +140,8 @@ export default class ShareService {
 		await Note.save({ id: note.id, is_shared: 0 });
 	}
 
-	public shareUrl(share: StateShare): string {
-		return `${this.api().userContentBaseUrl()}/shares/${share.id}`;
+	public shareUrl(userId: string, share: StateShare): string {
+		return `${this.api().userContentBaseUrl(userId)}/shares/${share.id}`;
 	}
 
 	public get shares() {
diff --git a/packages/lib/testing/test-utils.ts b/packages/lib/testing/test-utils.ts
index 41e2f0ba9c..6073a05e84 100644
--- a/packages/lib/testing/test-utils.ts
+++ b/packages/lib/testing/test-utils.ts
@@ -577,7 +577,7 @@ async function initFileApi() {
 		// const joplinServerAuth = {
 		//     "email": "admin@localhost",
 		//     "password": "admin",
-		//     "baseUrl": "http://api-joplincloud.local:22300",
+		//     "baseUrl": "http://api.joplincloud.local:22300",
 		//     "userContentBaseUrl": ""
 		// }
 
diff --git a/packages/server/src/models/ShareModel.ts b/packages/server/src/models/ShareModel.ts
index 8f26d937e8..cb313f5638 100644
--- a/packages/server/src/models/ShareModel.ts
+++ b/packages/server/src/models/ShareModel.ts
@@ -5,6 +5,7 @@ import { unique } from '../utils/array';
 import { ErrorBadRequest, ErrorForbidden, ErrorNotFound } from '../utils/errors';
 import { setQueryParameters } from '../utils/urlUtils';
 import BaseModel, { AclAction, DeleteOptions, ValidateOptions } from './BaseModel';
+import { userIdFromUserContentUrl } from '../utils/routeUtils';
 
 export default class ShareModel extends BaseModel<Share> {
 
@@ -33,6 +34,19 @@ export default class ShareModel extends BaseModel<Share> {
 		}
 	}
 
+	public checkShareUrl(share: Share, shareUrl: string) {
+		if (this.baseUrl === this.userContentUrl) return; // OK
+
+		const userId = userIdFromUserContentUrl(shareUrl);
+		const shareUserId = share.owner_id.toLowerCase();
+
+		if (userId.length >= 10 && shareUserId.indexOf(userId) === 0) {
+			// OK
+		} else {
+			throw new ErrorBadRequest('Invalid origin (User Content)');
+		}
+	}
+
 	protected objectToApiOutput(object: Share): Share {
 		const output: Share = {};
 
diff --git a/packages/server/src/routes/index/shares.ts b/packages/server/src/routes/index/shares.ts
index 9000c78e0f..55499f1976 100644
--- a/packages/server/src/routes/index/shares.ts
+++ b/packages/server/src/routes/index/shares.ts
@@ -36,6 +36,8 @@ router.get('shares/:id', async (path: SubPath, ctx: AppContext) => {
 
 	const result = await renderItem(ctx, item, share);
 
+	ctx.models.share().checkShareUrl(share, ctx.URL.origin);
+
 	ctx.response.body = result.body;
 	ctx.response.set('Content-Type', result.mime);
 	ctx.response.set('Content-Length', result.size.toString());
diff --git a/packages/server/src/utils/routeUtils.ts b/packages/server/src/utils/routeUtils.ts
index 385a0d14ff..32472e1fa7 100644
--- a/packages/server/src/utils/routeUtils.ts
+++ b/packages/server/src/utils/routeUtils.ts
@@ -1,5 +1,5 @@
 import { baseUrl } from '../config';
-import { Item, ItemAddressingType } from '../db';
+import { Item, ItemAddressingType, Uuid } from '../db';
 import { ErrorBadRequest, ErrorForbidden, ErrorNotFound } from './errors';
 import Router from './Router';
 import { AppContext, HttpMethod, RouteType } from './types';
@@ -153,19 +153,26 @@ export function parseSubPath(basePath: string, p: string, rawPath: string = null
 	return output;
 }
 
-export function isValidOrigin(requestOrigin: string, endPointBaseUrl: string): boolean {
+export function isValidOrigin(requestOrigin: string, endPointBaseUrl: string, routeType: RouteType): boolean {
 	const host1 = (new URL(requestOrigin)).host;
 	const host2 = (new URL(endPointBaseUrl)).host;
-	return host1 === host2;
+
+	if (routeType === RouteType.UserContent) {
+		if (host1 === host2) return true;
+
+		const hostNoPrefix = host1.split('.').slice(1).join('.');
+		return hostNoPrefix === host2;
+	} else {
+		return host1 === host2;
+	}
+}
+
+export function userIdFromUserContentUrl(url: string): Uuid {
+	const s = (new URL(url)).hostname.split('.');
+	return s[0].toLowerCase();
 }
 
 export function routeResponseFormat(context: AppContext): RouteResponseFormat {
-	// const rawPath = context.path;
-	// if (match && match.route.responseFormat) return match.route.responseFormat;
-
-	// let path = rawPath;
-	// if (match) path = match.basePath ? match.basePath : match.subPath.raw;
-
 	const path = context.path;
 	return path.indexOf('api') === 0 || path.indexOf('/api') === 0 ? RouteResponseFormat.Json : RouteResponseFormat.Html;
 }
@@ -175,7 +182,7 @@ export async function execRequest(routes: Routers, ctx: AppContext) {
 	if (!match) throw new ErrorNotFound();
 
 	const endPoint = match.route.findEndPoint(ctx.request.method as HttpMethod, match.subPath.schema);
-	if (ctx.URL && !isValidOrigin(ctx.URL.origin, baseUrl(endPoint.type))) throw new ErrorNotFound('Invalid origin', 'invalidOrigin');
+	if (ctx.URL && !isValidOrigin(ctx.URL.origin, baseUrl(endPoint.type), endPoint.type)) throw new ErrorNotFound('Invalid origin', 'invalidOrigin');
 
 	// This is a generic catch-all for all private end points - if we
 	// couldn't get a valid session, we exit now. Individual end points