[backend] Compact LD-signed activities against well-known context to defend against spoofing attacks

packages/backend/src/queue/processors/inbox.ts

@@ -29,7 +29,7 @@ const logger = new Logger("inbox");
 // Processing when an activity arrives in the user's inbox
 export default async (job: Bull.Job<InboxJobData>): Promise<string> => {
 	const signature = job.data.signature; // HTTP-signature
-	const activity = job.data.activity;
+	let activity = job.data.activity;
 
 	//#region Log
 	const info = Object.assign({}, activity) as any;
@@ -155,6 +155,8 @@ export default async (job: Bull.Job<InboxJobData>): Promise<string> => {
 				return "skip: LD-Signatureの検証に失敗しました";
 			}
 
+			activity = await ldSignature.compactToWellKnown(activity);
+
 			// もう一度actorチェック
 			if (authUser.user.uri !== activity.actor) {
 				return `skip: LD-Signature user(${authUser.user.uri}) !== activity.actor(${activity.actor})`;

packages/backend/src/remote/activitypub/misc/contexts.ts

@@ -518,6 +518,52 @@ const activitystreams = {
 	},
 };
 
+export const WellKnownContext = {
+	"@context": [
+		"https://www.w3.org/ns/activitystreams",
+		"https://w3id.org/security/v1",
+		{
+			// as non-standards
+			manuallyApprovesFollowers: "as:manuallyApprovesFollowers",
+			movedTo: {
+				"@id": "https://www.w3.org/ns/activitystreams#movedTo",
+				"@type": "@id"
+			},
+			movedToUri: "as:movedTo",
+			sensitive: "as:sensitive",
+			Hashtag: "as:Hashtag",
+			quoteUri: "fedibird:quoteUri",
+			quoteUrl: "as:quoteUrl",
+			// Mastodon
+			toot: "http://joinmastodon.org/ns#",
+			Emoji: "toot:Emoji",
+			featured: "toot:featured",
+			discoverable: "toot:discoverable",
+			// schema
+			schema: "http://schema.org#",
+			PropertyValue: "schema:PropertyValue",
+			value: "schema:value",
+			// Misskey
+			misskey: "https://misskey-hub.net/ns#",
+			_misskey_content: "misskey:_misskey_content",
+			_misskey_quote: "misskey:_misskey_quote",
+			_misskey_reaction: "misskey:_misskey_reaction",
+			_misskey_votes: "misskey:_misskey_votes",
+			_misskey_talk: "misskey:_misskey_talk",
+			_misskey_summary: "misskey:_misskey_summary",
+			isCat: "misskey:isCat",
+			// Fedibird
+			fedibird: "http://fedibird.com/ns#",
+			// vcard
+			vcard: "http://www.w3.org/2006/vcard/ns#",
+			// litepub
+			litepub: "http://litepub.social/ns#",
+			EmojiReact: "litepub:EmojiReact",
+			EmojiReaction: "litepub:EmojiReaction",
+		},
+	],
+};
+
 export const CONTEXTS: Record<string, unknown> = {
 	"https://w3id.org/identity/v1": id_v1,
 	"https://w3id.org/security/v1": security_v1,

packages/backend/src/remote/activitypub/misc/ld-signature.ts

@@ -1,6 +1,6 @@
 import * as crypto from "node:crypto";
 import jsonld from "jsonld";
-import { CONTEXTS } from "./contexts.js";
+import { CONTEXTS, WellKnownContext } from "./contexts.js";
 import fetch from "node-fetch";
 import { httpAgent, httpsAgent } from "@/misc/fetch.js";
 
@@ -89,6 +89,13 @@ export class LdSignature {
 		});
 	}
 
+	public async compactToWellKnown(data: any): Promise<any> {
+		const options = { documentLoader: this.getLoader() };
+		const context = WellKnownContext as any;
+		delete data["signature"];
+		return await jsonld.compact(data, context, options);
+	}
+
 	private getLoader() {
 		return async (url: string): Promise<any> => {
 			if (!url.match("^https?://")) throw new Error(`Invalid URL ${url}`);

packages/backend/src/remote/activitypub/renderer/index.ts

@@ -4,6 +4,7 @@ import { getUserKeypair } from "@/misc/keypair-store.js";
 import type { User } from "@/models/entities/user.js";
 import { LdSignature } from "../misc/ld-signature.js";
 import type { IActivity } from "../type.js";
+import { WellKnownContext } from "@/remote/activitypub/misc/contexts.js";
 
 export const renderActivity = (x: any): IActivity | null => {
 	if (x == null) return null;
@@ -12,46 +13,7 @@ export const renderActivity = (x: any): IActivity | null => {
 		x.id = `${config.url}/${uuid()}`;
 	}
 
-	return Object.assign(
+	return Object.assign({}, WellKnownContext, x);
-		{
-			"@context": [
-				"https://www.w3.org/ns/activitystreams",
-				"https://w3id.org/security/v1",
-				{
-					// as non-standards
-					manuallyApprovesFollowers: "as:manuallyApprovesFollowers",
-					movedToUri: "as:movedTo",
-					sensitive: "as:sensitive",
-					Hashtag: "as:Hashtag",
-					quoteUri: "fedibird:quoteUri",
-					quoteUrl: "as:quoteUrl",
-					// Mastodon
-					toot: "http://joinmastodon.org/ns#",
-					Emoji: "toot:Emoji",
-					featured: "toot:featured",
-					discoverable: "toot:discoverable",
-					// schema
-					schema: "http://schema.org#",
-					PropertyValue: "schema:PropertyValue",
-					value: "schema:value",
-					// Misskey
-					misskey: "https://misskey-hub.net/ns#",
-					_misskey_content: "misskey:_misskey_content",
-					_misskey_quote: "misskey:_misskey_quote",
-					_misskey_reaction: "misskey:_misskey_reaction",
-					_misskey_votes: "misskey:_misskey_votes",
-					_misskey_talk: "misskey:_misskey_talk",
-					_misskey_summary: "misskey:_misskey_summary",
-					isCat: "misskey:isCat",
-					// Fedibird
-					fedibird: "http://fedibird.com/ns#",
-					// vcard
-					vcard: "http://www.w3.org/2006/vcard/ns#",
-				},
-			],
-		},
-		x,
-	);
 };
 
 export const attachLdSignature = async (