From b8fcd0dc331ce73994f85ce078c03509bb8cc5ea Mon Sep 17 00:00:00 2001
From: ThatOneCalculator <kainoa@t1c.dev>
Date: Sat, 15 Jul 2023 14:13:21 -0700
Subject: [PATCH] fix: :lock: prevent potential SSRF through media proxy

---
 packages/backend/src/misc/download-url.ts     |  3 +-
 .../backend/src/server/proxy/proxy-media.ts   | 36 +++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/packages/backend/src/misc/download-url.ts b/packages/backend/src/misc/download-url.ts
index 7fafb635b..b96871e72 100644
--- a/packages/backend/src/misc/download-url.ts
+++ b/packages/backend/src/misc/download-url.ts
@@ -21,9 +21,10 @@ export async function downloadUrl(url: string, path: string): Promise<void> {
 	const maxSize = config.maxFileSize || 262144000;
 
 	const req = got
-		.stream(url, {
+	.stream(url, {
 			headers: {
 				"User-Agent": config.userAgent,
+				"Host": new URL(url).hostname,
 			},
 			timeout: {
 				lookup: timeout,
diff --git a/packages/backend/src/server/proxy/proxy-media.ts b/packages/backend/src/server/proxy/proxy-media.ts
index a9c257bfe..b3bb03124 100644
--- a/packages/backend/src/server/proxy/proxy-media.ts
+++ b/packages/backend/src/server/proxy/proxy-media.ts
@@ -1,4 +1,6 @@
 import * as fs from "node:fs";
+import net from "node:net";
+import { promises } from "node:dns";
 import type Koa from "koa";
 import sharp from "sharp";
 import type { IImage } from "@/services/drive/image-processor.js";
@@ -19,6 +21,40 @@ export async function proxyMedia(ctx: Koa.Context) {
 		return;
 	}
 
+	const { hostname } = new URL(url);
+	let resolvedIps;
+	try {
+		resolvedIps = await promises.resolve(hostname);
+	} catch (error) {
+		ctx.status = 400;
+		ctx.body = { message: "Invalid URL" };
+		return;
+	}
+
+	const isSSRF = resolvedIps.some((ip) => {
+		if (net.isIPv4(ip)) {
+			const parts = ip.split(".").map(Number);
+			return (
+				parts[0] === 10 ||
+				(parts[0] === 172 && parts[1] >= 16 && parts[1] < 32) ||
+				(parts[0] === 192 && parts[1] === 168) ||
+				parts[0] === 127 ||
+				parts[0] === 0
+			);
+		} else if (net.isIPv6(ip)) {
+			return (
+				ip.startsWith("::") || ip.startsWith("fc00:") || ip.startsWith("fe80:")
+			);
+		}
+		return false;
+	});
+
+	if (isSSRF) {
+		ctx.status = 400;
+		ctx.body = { message: "Access to this URL is not allowed" };
+		return;
+	}
+
 	// Create temp file
 	const [path, cleanup] = await createTemp();