diff --git a/packages/backend/src/config.ts b/packages/backend/src/config.ts
index 3dc49c7eb6..69a6a36453 100644
--- a/packages/backend/src/config.ts
+++ b/packages/backend/src/config.ts
@@ -96,6 +96,7 @@ type Source = {
 	inboxJobMaxAttempts?: number;
 
 	mediaProxy?: string;
+	mediaProxySecret?: string;
 	proxyRemoteFiles?: boolean;
 	videoThumbnailGenerator?: string;
 
@@ -193,6 +194,7 @@ export type Config = {
 	frontendEmbedEntry: string;
 	frontendEmbedManifestExists: boolean;
 	mediaProxy: string;
+	mediaProxySecret: string;
 	externalMediaProxyEnabled: boolean;
 	videoThumbnailGenerator: string | null;
 	redis: RedisOptions & RedisOptionsSource;
@@ -333,6 +335,7 @@ export function loadConfig(): Config {
 		attachLdSignatureForRelays: config.attachLdSignatureForRelays ?? true,
 		checkActivityPubGetSignature: config.checkActivityPubGetSignature,
 		mediaProxy: externalMediaProxy ?? internalMediaProxy,
+		mediaProxySecret: config.mediaProxySecret,
 		externalMediaProxyEnabled: externalMediaProxy !== null && externalMediaProxy !== internalMediaProxy,
 		videoThumbnailGenerator: config.videoThumbnailGenerator ?
 			config.videoThumbnailGenerator.endsWith('/') ? config.videoThumbnailGenerator.substring(0, config.videoThumbnailGenerator.length - 1) : config.videoThumbnailGenerator
diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index 42ee5bc58a..25d548b7ea 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -249,10 +249,13 @@ export class ApRendererService {
 	}
 
 	@bindThis
-	public renderImage(file: MiDriveFile): IApImage {
+	public renderImage(file: MiDriveFile, mode: 'avatar' | 'banner' = 'avatar'): IApImage {
 		return {
 			type: 'Image',
-			url: this.driveFileEntityService.getPublicUrl(file),
+			url: this.driveFileEntityService.getProxiedUrl(
+				this.driveFileEntityService.getPublicUrl(file)
+				mode,
+			),
 			sensitive: file.isSensitive,
 			name: file.comment,
 		};
@@ -517,8 +520,8 @@ export class ApRendererService {
 			summary: profile.description ? this.mfmService.toHtml(mfm.parse(profile.description)) : null,
 			_misskey_summary: profile.description,
 			_misskey_followedMessage: profile.followedMessage,
-			icon: avatar ? this.renderImage(avatar) : null,
-			image: banner ? this.renderImage(banner) : null,
+			icon: avatar ? this.renderImage(avatar, 'avatar') : null,
+			image: banner ? this.renderImage(banner, 'banner') : null,
 			backgroundUrl: background ? this.renderImage(background) : null,
 			tag,
 			manuallyApprovesFollowers: user.isLocked,
diff --git a/packages/backend/src/core/entities/DriveFileEntityService.ts b/packages/backend/src/core/entities/DriveFileEntityService.ts
index c485555f90..bab4246662 100644
--- a/packages/backend/src/core/entities/DriveFileEntityService.ts
+++ b/packages/backend/src/core/entities/DriveFileEntityService.ts
@@ -3,6 +3,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
+import * as crypto from 'node:crypto';
 import { forwardRef, Inject, Injectable } from '@nestjs/common';
 import { In } from 'typeorm';
 import { DI } from '@/di-symbols.js';
@@ -74,12 +75,16 @@ export class DriveFileEntityService {
 	}
 
 	@bindThis
-	private getProxiedUrl(url: string, mode?: 'static' | 'avatar'): string {
+	public getProxiedUrl(url: string, mode?: 'static' | 'avatar' | 'banner'): string {
+		const signature = crypto.createHmac('sha256', this.config.mediaProxySecret)
+			 .update(url)
+			 .digest('hex')[8];
 		return appendQuery(
 			`${this.config.mediaProxy}/${mode ?? 'image'}.webp`,
 			query({
 				url,
 				...(mode ? { [mode]: '1' } : {}),
+				sign: signature
 			}),
 		);
 	}
diff --git a/packages/backend/src/server/FileServerService.ts b/packages/backend/src/server/FileServerService.ts
index 1a4d0cb48f..6caa935ccc 100644
--- a/packages/backend/src/server/FileServerService.ts
+++ b/packages/backend/src/server/FileServerService.ts
@@ -4,6 +4,7 @@
  */
 
 import * as fs from 'node:fs';
+import * as crypto from 'node:crypto';
 import { fileURLToPath } from 'node:url';
 import { dirname } from 'node:path';
 import { Inject, Injectable } from '@nestjs/common';
@@ -317,10 +318,13 @@ export class FileServerService {
 			);
 		}
 
-		if (!request.headers['user-agent']) {
-			throw new StatusError('User-Agent is required', 400, 'User-Agent is required');
-		} else if (request.headers['user-agent'].toLowerCase().indexOf('misskey/') !== -1) {
-			throw new StatusError('Refusing to proxy a request from another proxy', 403, 'Proxy is recursive');
+		const signature = crypto.createHmac('sha256', this.config.mediaProxySecret)
+			 .update(url)
+			 .digest('hex')[8];
+
+		if (signature !== request.params.sign) {
+			reply.code(403);
+			return;
 		}
 
 		// Create temp file