Compact LD-signed activities against well-known context

This should defend against some spoofing attacks, see also
https://nvd.nist.gov/vuln/detail/CVE-2022-24307 for Mastodon,
febb499fcb
from Iceshrimp and
e790d6be90
for Firefish

Thanks to @tesaguri@fedibird.com for reporting and providing the patch.

packages/backend/src/core/activitypub/ApRendererService.ts

@@ -31,6 +31,7 @@ import { IdService } from '@/core/IdService.js';
 import { MetaService } from '../MetaService.js';
 import { LdSignatureService } from './LdSignatureService.js';
 import { ApMfmService } from './ApMfmService.js';
+import { CONTEXT } from './misc/contexts.js';
 import type { IAccept, IActivity, IAdd, IAnnounce, IApDocument, IApEmoji, IApHashtag, IApImage, IApMention, IBlock, ICreate, IDelete, IFlag, IFollow, IKey, ILike, IMove, IObject, IPost, IQuestion, IReject, IRemove, ITombstone, IUndo, IUpdate } from './type.js';
 
 @Injectable()
@@ -785,48 +786,7 @@ export class ApRendererService {
 			x.id = `${this.config.url}/${randomUUID()}`;
 		}
 
-		return Object.assign({
-			'@context': [
-				'https://www.w3.org/ns/activitystreams',
-				'https://w3id.org/security/v1',
-				{
-					Key: 'sec:Key',
-					// as non-standards
-					manuallyApprovesFollowers: 'as:manuallyApprovesFollowers',
-					sensitive: 'as:sensitive',
-					Hashtag: 'as:Hashtag',
-					quoteUrl: 'as:quoteUrl',
-					fedibird: 'http://fedibird.com/ns#',
-					quoteUri: 'fedibird:quoteUri',
-					// 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_summary': 'misskey:_misskey_summary',
-					'isCat': 'misskey:isCat',
-					// Firefish
-					firefish: 'https://joinfirefish.org/ns#',
-					speakAsCat: 'firefish:speakAsCat',
-					// Sharkey
-					sharkey: 'https://joinsharkey.org/ns#',
-					backgroundUrl: 'sharkey:backgroundUrl',
-					listenbrainz: 'sharkey:listenbrainz',
-					// vcard
-					vcard: 'http://www.w3.org/2006/vcard/ns#',
-				},
-			],
-		}, x as T & { id: string });
+		return Object.assign({ '@context': CONTEXT }, x as T & { id: string });
 	}
 
 	@bindThis

packages/backend/src/core/activitypub/LdSignatureService.ts

@@ -88,6 +88,16 @@ class LdSignature {
 		return verifyData;
 	}
 
+	@bindThis
+	public async compact(data: any, context: any = CONTEXT): Promise<JsonLdDocument> {
+		const customLoader = this.getLoader();
+		// XXX: Importing jsonld dynamically since Jest frequently fails to import it statically
+		// https://github.com/misskey-dev/misskey/pull/9894#discussion_r1103753595
+		return (await import('jsonld')).default.compact(data, context, {
+			documentLoader: customLoader,
+		});
+	}
+
 	@bindThis
 	public async normalize(data: JsonLdDocument): Promise<string> {
 		const customLoader = this.getLoader();

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

@@ -3,7 +3,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import type { JsonLd } from 'jsonld/jsonld-spec.js';
+import type { Context, JsonLd } from 'jsonld/jsonld-spec.js';
 
 /* eslint:disable:quotemark indent */
 const id_v1 = {
@@ -526,6 +526,50 @@ const activitystreams = {
 	},
 } satisfies JsonLd;
 
+const context_iris = [
+	'https://www.w3.org/ns/activitystreams',
+	'https://w3id.org/security/v1',
+];
+
+const extension_context_definition = {
+	Key: 'sec:Key',
+	// as non-standards
+	manuallyApprovesFollowers: 'as:manuallyApprovesFollowers',
+	sensitive: 'as:sensitive',
+	Hashtag: 'as:Hashtag',
+	quoteUrl: 'as:quoteUrl',
+	fedibird: 'http://fedibird.com/ns#',
+	quoteUri: 'fedibird:quoteUri',
+	// 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_summary': 'misskey:_misskey_summary',
+	'isCat': 'misskey:isCat',
+	// Firefish
+	firefish: 'https://joinfirefish.org/ns#',
+	speakAsCat: 'firefish:speakAsCat',
+	// Sharkey
+	sharkey: 'https://joinsharkey.org/ns#',
+	backgroundUrl: 'sharkey:backgroundUrl',
+	listenbrainz: 'sharkey:listenbrainz',
+	// vcard
+	vcard: 'http://www.w3.org/2006/vcard/ns#',
+} satisfies Context;
+
+export const CONTEXT: (string | Context)[] = [...context_iris, extension_context_definition];
+
 export const CONTEXTS: Record<string, JsonLd> = {
 	'https://w3id.org/identity/v1': id_v1,
 	'https://w3id.org/security/v1': security_v1,

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

@@ -15,6 +15,7 @@ import InstanceChart from '@/core/chart/charts/instance.js';
 import ApRequestChart from '@/core/chart/charts/ap-request.js';
 import FederationChart from '@/core/chart/charts/federation.js';
 import { getApId } from '@/core/activitypub/type.js';
+import type { IActivity } from '@/core/activitypub/type.js';
 import type { MiRemoteUser } from '@/models/User.js';
 import type { MiUserPublickey } from '@/models/UserPublickey.js';
 import { ApDbResolverService } from '@/core/activitypub/ApDbResolverService.js';
@@ -52,7 +53,7 @@ export class InboxProcessorService {
 	@bindThis
 	public async process(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);
@@ -150,6 +151,17 @@ export class InboxProcessorService {
 					throw new Bull.UnrecoverableError('skip: LD-Signatureの検証に失敗しました');
 				}
 
+				// アクティビティを正規化
+				delete activity.signature;
+				try {
+					activity = await ldSignature.compact(activity) as IActivity;
+				} catch (e) {
+					throw new Bull.UnrecoverableError(`skip: failed to compact activity: ${e}`);
+				}
+				// TODO: 元のアクティビティと非互換な形に正規化される場合は転送をスキップする
+				// https://github.com/mastodon/mastodon/blob/664b0ca/app/services/activitypub/process_collection_service.rb#L24-L29
+				activity.signature = ldSignature;
+
 				// もう一度actorチェック
 				if (authUser.user.uri !== activity.actor) {
 					throw new Bull.UnrecoverableError(`skip: LD-Signature user(${authUser.user.uri}) !== activity.actor(${activity.actor})`);