Merge commit from fork

* enhance: Add a few validation fixes from Sharkey

See the original MR on the GitLab instance:
https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/484

Co-Authored-By: Dakkar <dakkar@thenautilus.net>

* fix: primitive 2: acceptance of cross-origin alternate

Co-Authored-By: Laura Hausmann <laura@hausmann.dev>

* fix: primitive 3: validation of non-final url

* fix: primitive 4: missing same-origin identifier validation of collection-wrapped activities

* fix: primitives 5 & 8: reject activities with non
string identifiers

Co-Authored-By: Laura Hausmann <laura@hausmann.dev>

* fix: primitive 6: reject anonymous objects that were fetched by their id

* fix: primitives 9, 10 & 11: http signature validation
doesn't enforce required headers or specify auth header name

Co-Authored-By: Laura Hausmann <laura@hausmann.dev>

* fix: primitive 14: improper validation of outbox, followers, following & shared inbox collections

* fix: code style for primitive 14

* fix: primitive 15: improper same-origin validation for
note uri and url

Co-Authored-By: Laura Hausmann <laura@hausmann.dev>

* fix: primitive 16: improper same-origin validation for user uri and url

* fix: primitive 17: note same-origin identifier validation can be bypassed by wrapping the id in an array

* fix: code style for primitive 17

* fix: check attribution against actor in notes

While this isn't strictly required to fix the exploits at hand, this
mirrors the fix in `ApQuestionService` for GHSA-5h8r-gq97-xv69, as a
preemptive countermeasure.

* fix: primitive 18: `ap/get` bypasses access checks

One might argue that we could make this one actually preform access
checks against the returned activity object, but I feel like that's a
lot more work than just restricting it to administrators, since, to me
at least, it seems more like a debugging tool than anything else.

* fix: primitive 19 & 20: respect blocks and hide more

Ideally, the user property should also be hidden (as leaving it in leaks
information slightly), but given the schema of the note endpoint, I
don't think that would be possible without introducing some kind of
"ghost" user, who is attributed for posts by users who have you blocked.

* fix: primitives 21, 22, and 23: reuse resolver

This also increases the default `recursionLimit` for `Resolver`, as it
theoretically will go higher that it previously would and could possibly
fail on non-malicious collection activities.

* fix: primitives 25-33: proper local instance checks

* revert: fix: primitive 19 & 20

This reverts commit 465a9fe6591de90f78bd3d084e3c01e65dc3cf3c.

---------

Co-authored-by: Dakkar <dakkar@thenautilus.net>
Co-authored-by: Laura Hausmann <laura@hausmann.dev>
Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

15 files changed, 227 insertions, 76 deletions

diff --git a/packages/backend/src/core/HttpRequestService.ts b/packages/backend/src/core/HttpRequestService.ts
index 7f3cac7c58..08e9f46b2d 100644
--- a/packages/backend/src/core/HttpRequestService.ts
+++ b/packages/backend/src/core/HttpRequestService.ts
@@ -15,6 +15,7 @@ import type { Config } from '@/config.js';
 import { StatusError } from '@/misc/status-error.js';
 import { bindThis } from '@/decorators.js';
 import { validateContentTypeSetAsActivityPub } from '@/core/activitypub/misc/validator.js';
+import { assertActivityMatchesUrls } from '@/core/activitypub/misc/check-against-url.js';
 import type { IObject } from '@/core/activitypub/type.js';
 import type { Response } from 'node-fetch';
 import type { URL } from 'node:url';
@@ -125,7 +126,12 @@ export class HttpRequestService {
 			validators: [validateContentTypeSetAsActivityPub],
 		});
 
-		return await res.json() as IObject;
+		const finalUrl = res.url; // redirects may have been involved
+		const activity = await res.json() as IObject;
+
+		assertActivityMatchesUrls(activity, [finalUrl]);
+
+		return activity;
 	}
 
 	@bindThis
diff --git a/packages/backend/src/core/RemoteUserResolveService.ts b/packages/backend/src/core/RemoteUserResolveService.ts
index f5a55eb8bc..678da0cfa6 100644
--- a/packages/backend/src/core/RemoteUserResolveService.ts
+++ b/packages/backend/src/core/RemoteUserResolveService.ts
@@ -54,9 +54,9 @@ export class RemoteUserResolveService {
 			}) as MiLocalUser;
 		}
 
-		host = this.utilityService.toPuny(host);
+		host = this.utilityService.punyHost(host);
 
-		if (this.config.host === host) {
+		if (host === this.utilityService.toPuny(this.config.host)) {
 			this.logger.info(`return local user: ${usernameLower}`);
 			return await this.usersRepository.findOneBy({ usernameLower, host: IsNull() }).then(u => {
 				if (u == null) {
diff --git a/packages/backend/src/core/UtilityService.ts b/packages/backend/src/core/UtilityService.ts
index 86082ccdcd..9a2ba72ed3 100644
--- a/packages/backend/src/core/UtilityService.ts
+++ b/packages/backend/src/core/UtilityService.ts
@@ -35,6 +35,11 @@ export class UtilityService {
 	}
 
 	@bindThis
+	public isUriLocal(uri: string): boolean {
+		return this.punyHost(uri) === this.toPuny(this.config.host);
+	}
+
+	@bindThis
 	public isBlockedHost(blockedHosts: string[], host: string | null): boolean {
 		if (host == null) return false;
 		return blockedHosts.some(x => `.${host.toLowerCase()}`.endsWith(`.${x}`));
@@ -96,7 +101,7 @@ export class UtilityService {
 	@bindThis
 	public extractDbHost(uri: string): string {
 		const url = new URL(uri);
-		return this.toPuny(url.hostname);
+		return this.toPuny(url.host);
 	}
 
 	@bindThis
@@ -111,6 +116,13 @@ export class UtilityService {
 	}
 
 	@bindThis
+	public punyHost(url: string): string {
+		const urlObj = new URL(url);
+		const host = `${this.toPuny(urlObj.hostname)}${urlObj.port.length > 0 ? ':' + urlObj.port : ''}`;
+		return host;
+	}
+
+	@bindThis
 	public isFederationAllowedHost(host: string): boolean {
 		if (this.meta.federation === 'none') return false;
 		if (this.meta.federation === 'specified' && !this.meta.federationHosts.some(x => `.${host.toLowerCase()}`.endsWith(`.${x}`))) return false;
diff --git a/packages/backend/src/core/activitypub/ApDbResolverService.ts b/packages/backend/src/core/activitypub/ApDbResolverService.ts
index 4192e8659a..5c16744a77 100644
--- a/packages/backend/src/core/activitypub/ApDbResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApDbResolverService.ts
@@ -10,6 +10,7 @@ import type { Config } from '@/config.js';
 import { MemoryKVCache } from '@/misc/cache.js';
 import type { MiUserPublickey } from '@/models/UserPublickey.js';
 import { CacheService } from '@/core/CacheService.js';
+import { UtilityService } from '@/core/UtilityService.js';
 import type { MiNote } from '@/models/Note.js';
 import { bindThis } from '@/decorators.js';
 import { MiLocalUser, MiRemoteUser } from '@/models/User.js';
@@ -53,6 +54,7 @@ export class ApDbResolverService implements OnApplicationShutdown {
 
 		private cacheService: CacheService,
 		private apPersonService: ApPersonService,
+		private utilityService: UtilityService,
 	) {
 		this.publicKeyCache = new MemoryKVCache<MiUserPublickey | null>(1000 * 60 * 60 * 12); // 12h
 		this.publicKeyByUserIdCache = new MemoryKVCache<MiUserPublickey | null>(1000 * 60 * 60 * 12); // 12h
@@ -63,7 +65,9 @@ export class ApDbResolverService implements OnApplicationShutdown {
 		const separator = '/';
 
 		const uri = new URL(getApId(value));
-		if (uri.origin !== this.config.url) return { local: false, uri: uri.href };
+		if (this.utilityService.toPuny(uri.host) !== this.utilityService.toPuny(this.config.host)) {
+			return { local: false, uri: uri.href };
+		}
 
 		const [, type, id, ...rest] = uri.pathname.split(separator);
 		return {
diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index 376c9c0151..8e8ec223cb 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -89,15 +89,26 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	public async performActivity(actor: MiRemoteUser, activity: IObject): Promise<string | void> {
+	public async performActivity(actor: MiRemoteUser, activity: IObject, resolver?: Resolver): Promise<string | void> {
 		let result = undefined as string | void;
 		if (isCollectionOrOrderedCollection(activity)) {
 			const results = [] as [string, string | void][];
-			const resolver = this.apResolverService.createResolver();
-			for (const item of toArray(isCollection(activity) ? activity.items : activity.orderedItems)) {
+			// eslint-disable-next-line no-param-reassign
+			resolver ??= this.apResolverService.createResolver();
+
+			const items = toArray(isCollection(activity) ? activity.items : activity.orderedItems);
+			if (items.length >= resolver.getRecursionLimit()) {
+				throw new Error(`skipping activity: collection would surpass recursion limit: ${this.utilityService.extractDbHost(actor.uri)}`);
+			}
+
+			for (const item of items) {
 				const act = await resolver.resolve(item);
+				if (act.id == null || this.utilityService.extractDbHost(act.id) !== this.utilityService.extractDbHost(actor.uri)) {
+					this.logger.debug('skipping activity: activity id is null or mismatching');
+					continue;
+				}
 				try {
-					results.push([getApId(item), await this.performOneActivity(actor, act)]);
+					results.push([getApId(item), await this.performOneActivity(actor, act, resolver)]);
 				} catch (err) {
 					if (err instanceof Error || typeof err === 'string') {
 						this.logger.error(err);
@@ -112,7 +123,7 @@ export class ApInboxService {
 				result = results.map(([id, reason]) => `${id}: ${reason}`).join('\n');
 			}
 		} else {
-			result = await this.performOneActivity(actor, activity);
+			result = await this.performOneActivity(actor, activity, resolver);
 		}
 
 		// ついでにリモートユーザーの情報が古かったら更新しておく
@@ -127,37 +138,37 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	public async performOneActivity(actor: MiRemoteUser, activity: IObject): Promise<string | void> {
+	public async performOneActivity(actor: MiRemoteUser, activity: IObject, resolver?: Resolver): Promise<string | void> {
 		if (actor.isSuspended) return;
 
 		if (isCreate(activity)) {
-			return await this.create(actor, activity);
+			return await this.create(actor, activity, resolver);
 		} else if (isDelete(activity)) {
 			return await this.delete(actor, activity);
 		} else if (isUpdate(activity)) {
-			return await this.update(actor, activity);
+			return await this.update(actor, activity, resolver);
 		} else if (isFollow(activity)) {
 			return await this.follow(actor, activity);
 		} else if (isAccept(activity)) {
-			return await this.accept(actor, activity);
+			return await this.accept(actor, activity, resolver);
 		} else if (isReject(activity)) {
-			return await this.reject(actor, activity);
+			return await this.reject(actor, activity, resolver);
 		} else if (isAdd(activity)) {
-			return await this.add(actor, activity);
+			return await this.add(actor, activity, resolver);
 		} else if (isRemove(activity)) {
-			return await this.remove(actor, activity);
+			return await this.remove(actor, activity, resolver);
 		} else if (isAnnounce(activity)) {
-			return await this.announce(actor, activity);
+			return await this.announce(actor, activity, resolver);
 		} else if (isLike(activity)) {
 			return await this.like(actor, activity);
 		} else if (isUndo(activity)) {
-			return await this.undo(actor, activity);
+			return await this.undo(actor, activity, resolver);
 		} else if (isBlock(activity)) {
 			return await this.block(actor, activity);
 		} else if (isFlag(activity)) {
 			return await this.flag(actor, activity);
 		} else if (isMove(activity)) {
-			return await this.move(actor, activity);
+			return await this.move(actor, activity, resolver);
 		} else {
 			return `unrecognized activity type: ${activity.type}`;
 		}
@@ -199,12 +210,13 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async accept(actor: MiRemoteUser, activity: IAccept): Promise<string> {
+	private async accept(actor: MiRemoteUser, activity: IAccept, resolver?: Resolver): Promise<string> {
 		const uri = activity.id ?? activity;
 
 		this.logger.info(`Accept: ${uri}`);
 
-		const resolver = this.apResolverService.createResolver();
+		// eslint-disable-next-line no-param-reassign
+		resolver ??= this.apResolverService.createResolver();
 
 		const object = await resolver.resolve(activity.object).catch(err => {
 			this.logger.error(`Resolution failed: ${err}`);
@@ -241,7 +253,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async add(actor: MiRemoteUser, activity: IAdd): Promise<string | void> {
+	private async add(actor: MiRemoteUser, activity: IAdd, resolver?: Resolver): Promise<string | void> {
 		if (actor.uri !== activity.actor) {
 			return 'invalid actor';
 		}
@@ -251,7 +263,7 @@ export class ApInboxService {
 		}
 
 		if (activity.target === actor.featured) {
-			const note = await this.apNoteService.resolveNote(activity.object);
+			const note = await this.apNoteService.resolveNote(activity.object, { resolver });
 			if (note == null) return 'note not found';
 			await this.notePiningService.addPinned(actor, note.id);
 			return;
@@ -261,12 +273,13 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async announce(actor: MiRemoteUser, activity: IAnnounce): Promise<string | void> {
+	private async announce(actor: MiRemoteUser, activity: IAnnounce, resolver?: Resolver): Promise<string | void> {
 		const uri = getApId(activity);
 
 		this.logger.info(`Announce: ${uri}`);
 
-		const resolver = this.apResolverService.createResolver();
+		// eslint-disable-next-line no-param-reassign
+		resolver ??= this.apResolverService.createResolver();
 
 		if (!activity.object) return 'skip: activity has no object property';
 		const targetUri = getApId(activity.object);
@@ -283,7 +296,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async announceNote(actor: MiRemoteUser, activity: IAnnounce, target: IPost): Promise<string | void> {
+	private async announceNote(actor: MiRemoteUser, activity: IAnnounce, target: IPost, resolver?: Resolver): Promise<string | void> {
 		const uri = getApId(activity);
 
 		if (actor.isSuspended) {
@@ -305,7 +318,7 @@ export class ApInboxService {
 			// Announce対象をresolve
 			let renote;
 			try {
-				renote = await this.apNoteService.resolveNote(target);
+				renote = await this.apNoteService.resolveNote(target, { resolver });
 				if (renote == null) return 'announce target is null';
 			} catch (err) {
 				// 対象が4xxならスキップ
@@ -324,7 +337,7 @@ export class ApInboxService {
 
 			this.logger.info(`Creating the (Re)Note: ${uri}`);
 
-			const activityAudience = await this.apAudienceService.parseAudience(actor, activity.to, activity.cc);
+			const activityAudience = await this.apAudienceService.parseAudience(actor, activity.to, activity.cc, resolver);
 			const createdAt = activity.published ? new Date(activity.published) : null;
 
 			if (createdAt && createdAt < this.idService.parse(renote.id).date) {
@@ -362,7 +375,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async create(actor: MiRemoteUser, activity: ICreate): Promise<string | void> {
+	private async create(actor: MiRemoteUser, activity: ICreate, resolver?: Resolver): Promise<string | void> {
 		const uri = getApId(activity);
 
 		this.logger.info(`Create: ${uri}`);
@@ -387,7 +400,8 @@ export class ApInboxService {
 			activity.object.attributedTo = activity.actor;
 		}
 
-		const resolver = this.apResolverService.createResolver();
+		// eslint-disable-next-line no-param-reassign
+		resolver ??= this.apResolverService.createResolver();
 
 		const object = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
@@ -414,6 +428,8 @@ export class ApInboxService {
 				if (this.utilityService.extractDbHost(actor.uri) !== this.utilityService.extractDbHost(note.id)) {
 					return 'skip: host in actor.uri !== note.id';
 				}
+			} else {
+				return 'skip: note.id is not a string';
 			}
 		}
 
@@ -423,7 +439,7 @@ export class ApInboxService {
 			const exist = await this.apNoteService.fetchNote(note);
 			if (exist) return 'skip: note exists';
 
-			await this.apNoteService.createNote(note, resolver, silent);
+			await this.apNoteService.createNote(note, actor, resolver, silent);
 			return 'ok';
 		} catch (err) {
 			if (err instanceof StatusError && !err.isRetryable) {
@@ -555,12 +571,13 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async reject(actor: MiRemoteUser, activity: IReject): Promise<string> {
+	private async reject(actor: MiRemoteUser, activity: IReject, resolver?: Resolver): Promise<string> {
 		const uri = activity.id ?? activity;
 
 		this.logger.info(`Reject: ${uri}`);
 
-		const resolver = this.apResolverService.createResolver();
+		// eslint-disable-next-line no-param-reassign
+		resolver ??= this.apResolverService.createResolver();
 
 		const object = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
@@ -597,7 +614,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async remove(actor: MiRemoteUser, activity: IRemove): Promise<string | void> {
+	private async remove(actor: MiRemoteUser, activity: IRemove, resolver?: Resolver): Promise<string | void> {
 		if (actor.uri !== activity.actor) {
 			return 'invalid actor';
 		}
@@ -607,7 +624,7 @@ export class ApInboxService {
 		}
 
 		if (activity.target === actor.featured) {
-			const note = await this.apNoteService.resolveNote(activity.object);
+			const note = await this.apNoteService.resolveNote(activity.object, { resolver });
 			if (note == null) return 'note not found';
 			await this.notePiningService.removePinned(actor, note.id);
 			return;
@@ -617,7 +634,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async undo(actor: MiRemoteUser, activity: IUndo): Promise<string> {
+	private async undo(actor: MiRemoteUser, activity: IUndo, resolver?: Resolver): Promise<string> {
 		if (actor.uri !== activity.actor) {
 			return 'invalid actor';
 		}
@@ -626,7 +643,8 @@ export class ApInboxService {
 
 		this.logger.info(`Undo: ${uri}`);
 
-		const resolver = this.apResolverService.createResolver();
+		// eslint-disable-next-line no-param-reassign
+		resolver ??= this.apResolverService.createResolver();
 
 		const object = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
@@ -750,14 +768,15 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async update(actor: MiRemoteUser, activity: IUpdate): Promise<string> {
+	private async update(actor: MiRemoteUser, activity: IUpdate, resolver?: Resolver): Promise<string> {
 		if (actor.uri !== activity.actor) {
 			return 'skip: invalid actor';
 		}
 
 		this.logger.debug('Update');
 
-		const resolver = this.apResolverService.createResolver();
+		// eslint-disable-next-line no-param-reassign
+		resolver ??= this.apResolverService.createResolver();
 
 		const object = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
@@ -776,11 +795,11 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async move(actor: MiRemoteUser, activity: IMove): Promise<string> {
+	private async move(actor: MiRemoteUser, activity: IMove, resolver?: Resolver): Promise<string> {
 		// fetch the new and old accounts
 		const targetUri = getApHrefNullable(activity.target);
 		if (!targetUri) return 'skip: invalid activity target';
 
-		return await this.apPersonService.updatePerson(actor.uri) ?? 'skip: nothing to do';
+		return await this.apPersonService.updatePerson(actor.uri, resolver) ?? 'skip: nothing to do';
 	}
 }
diff --git a/packages/backend/src/core/activitypub/ApRequestService.ts b/packages/backend/src/core/activitypub/ApRequestService.ts
index c7d19adfd5..8c3b7295e4 100644
--- a/packages/backend/src/core/activitypub/ApRequestService.ts
+++ b/packages/backend/src/core/activitypub/ApRequestService.ts
@@ -11,11 +11,14 @@ import { DI } from '@/di-symbols.js';
 import type { Config } from '@/config.js';
 import type { MiUser } from '@/models/User.js';
 import { UserKeypairService } from '@/core/UserKeypairService.js';
+import { UtilityService } from '@/core/UtilityService.js';
 import { HttpRequestService } from '@/core/HttpRequestService.js';
 import { LoggerService } from '@/core/LoggerService.js';
 import { bindThis } from '@/decorators.js';
 import type Logger from '@/logger.js';
 import { validateContentTypeSetAsActivityPub } from '@/core/activitypub/misc/validator.js';
+import { assertActivityMatchesUrls } from '@/core/activitypub/misc/check-against-url.js';
+import type { IObject } from './type.js';
 
 type Request = {
 	url: string;
@@ -145,6 +148,7 @@ export class ApRequestService {
 		private userKeypairService: UserKeypairService,
 		private httpRequestService: HttpRequestService,
 		private loggerService: LoggerService,
+		private utilityService: UtilityService,
 	) {
 		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
 		this.logger = this.loggerService?.getLogger('ap-request'); // なぜか TypeError: Cannot read properties of undefined (reading 'getLogger') と言われる
@@ -238,7 +242,7 @@ export class ApRequestService {
 				const alternate = document.querySelector('head > link[rel="alternate"][type="application/activity+json"]');
 				if (alternate) {
 					const href = alternate.getAttribute('href');
-					if (href) {
+					if (href && this.utilityService.punyHost(url) === this.utilityService.punyHost(href)) {
 						return await this.signedGet(href, user, false);
 					}
 				}
@@ -251,7 +255,11 @@ export class ApRequestService {
 		//#endregion
 
 		validateContentTypeSetAsActivityPub(res);
+		const finalUrl = res.url; // redirects may have been involved
+		const activity = await res.json() as IObject;
 
-		return await res.json();
+		assertActivityMatchesUrls(activity, [finalUrl]);
+
+		return activity;
 	}
 }
diff --git a/packages/backend/src/core/activitypub/ApResolverService.ts b/packages/backend/src/core/activitypub/ApResolverService.ts
index ca35608d9b..b0b35274ea 100644
--- a/packages/backend/src/core/activitypub/ApResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApResolverService.ts
@@ -41,7 +41,7 @@ export class Resolver {
 		private apRendererService: ApRendererService,
 		private apDbResolverService: ApDbResolverService,
 		private loggerService: LoggerService,
-		private recursionLimit = 100,
+		private recursionLimit = 256,
 	) {
 		this.history = new Set();
 		this.logger = this.loggerService.getLogger('ap-resolve');
@@ -53,6 +53,11 @@ export class Resolver {
 	}
 
 	@bindThis
+	public getRecursionLimit(): number {
+		return this.recursionLimit;
+	}
+
+	@bindThis
 	public async resolveCollection(value: string | IObject): Promise<ICollection | IOrderedCollection> {
 		const collection = typeof value === 'string'
 			? await this.resolve(value)
@@ -113,6 +118,18 @@ export class Resolver {
 			throw new Error('invalid response');
 		}
 
+		// HttpRequestService / ApRequestService have already checked that
+		// `object.id` or `object.url` matches the URL used to fetch the
+		// object after redirects; here we double-check that no redirects
+		// bounced between hosts
+		if (object.id == null) {
+			throw new Error('invalid AP object: missing id');
+		}
+
+		if (this.utilityService.punyHost(object.id) !== this.utilityService.punyHost(value)) {
+			throw new Error(`invalid AP object ${value}: id ${object.id} has different host`);
+		}
+
 		return object;
 	}
 
diff --git a/packages/backend/src/core/activitypub/misc/check-against-url.ts b/packages/backend/src/core/activitypub/misc/check-against-url.ts
new file mode 100644
index 0000000000..78ba891a2e
--- /dev/null
+++ b/packages/backend/src/core/activitypub/misc/check-against-url.ts
@@ -0,0 +1,19 @@
+/*
+ * SPDX-FileCopyrightText: dakkar and sharkey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import type { IObject } from '../type.js';
+
+export function assertActivityMatchesUrls(activity: IObject, urls: string[]) {
+	const idOk = activity.id !== undefined && urls.includes(activity.id);
+
+	// technically `activity.url` could be an `ApObject = IObject |
+	// string | (IObject | string)[]`, but if it's a complicated thing
+	// and the `activity.id` doesn't match, I think we're fine
+	// rejecting the activity
+	const urlOk = typeof(activity.url) === 'string' && urls.includes(activity.url);
+
+	if (!idOk && !urlOk) {
+		throw new Error(`bad Activity: neither id(${activity?.id}) nor url(${activity?.url}) match location(${urls})`);
+	}
+}
diff --git a/packages/backend/src/core/activitypub/models/ApNoteService.ts b/packages/backend/src/core/activitypub/models/ApNoteService.ts
index 2d333b3634..eb2e771a38 100644
--- a/packages/backend/src/core/activitypub/models/ApNoteService.ts
+++ b/packages/backend/src/core/activitypub/models/ApNoteService.ts
@@ -77,7 +77,7 @@ export class ApNoteService {
 	}
 
 	@bindThis
-	public validateNote(object: IObject, uri: string): Error | null {
+	public validateNote(object: IObject, uri: string, actor?: MiRemoteUser): Error | null {
 		const expectHost = this.utilityService.extractDbHost(uri);
 		const apType = getApType(object);
 
@@ -98,6 +98,14 @@ export class ApNoteService {
 			return new IdentifiableError('d450b8a9-48e4-4dab-ae36-f4db763fda7c', 'invalid Note: published timestamp is malformed');
 		}
 
+		if (actor) {
+			const attribution = (object.attributedTo) ? getOneApId(object.attributedTo) : actor.uri;
+
+			if (attribution !== actor.uri) {
+				return new IdentifiableError('d450b8a9-48e4-4dab-ae36-f4db763fda7c', `invalid Note: attribution does not match the actor that send it. attribution: ${attribution}, actor: ${actor.uri}`);
+			}
+		}
+
 		return null;
 	}
 
@@ -115,14 +123,14 @@ export class ApNoteService {
 	 * Noteを作成します。
 	 */
 	@bindThis
-	public async createNote(value: string | IObject, resolver?: Resolver, silent = false): Promise<MiNote | null> {
+	public async createNote(value: string | IObject, actor?: MiRemoteUser, resolver?: Resolver, silent = false): Promise<MiNote | null> {
 		// eslint-disable-next-line no-param-reassign
 		if (resolver == null) resolver = this.apResolverService.createResolver();
 
 		const object = await resolver.resolve(value);
 
 		const entryUri = getApId(value);
-		const err = this.validateNote(object, entryUri);
+		const err = this.validateNote(object, entryUri, actor);
 		if (err) {
 			this.logger.error(err.message, {
 				resolver: { history: resolver.getHistory() },
@@ -136,14 +144,24 @@ export class ApNoteService {
 
 		this.logger.debug(`Note fetched: ${JSON.stringify(note, null, 2)}`);
 
-		if (note.id && !checkHttps(note.id)) {
+		if (note.id == null) {
+			throw new Error('Refusing to create note without id');
+		}
+
+		if (!checkHttps(note.id)) {
 			throw new Error('unexpected schema of note.id: ' + note.id);
 		}
 
 		const url = getOneApHrefNullable(note.url);
 
-		if (url && !checkHttps(url)) {
-			throw new Error('unexpected schema of note url: ' + url);
+		if (url != null) {
+			if (!checkHttps(url)) {
+				throw new Error('unexpected schema of note url: ' + url);
+			}
+
+			if (this.utilityService.punyHost(url) !== this.utilityService.punyHost(note.id)) {
+				throw new Error(`note url & uri host mismatch: note url: ${url}, note uri: ${note.id}`);
+			}
 		}
 
 		this.logger.info(`Creating the Note: ${note.id}`);
@@ -156,8 +174,9 @@ export class ApNoteService {
 		const uri = getOneApId(note.attributedTo);
 
 		// ローカルで投稿者を検索し、もし凍結されていたらスキップ
-		const cachedActor = await this.apPersonService.fetchPerson(uri) as MiRemoteUser;
-		if (cachedActor && cachedActor.isSuspended) {
+		// eslint-disable-next-line no-param-reassign
+		actor ??= await this.apPersonService.fetchPerson(uri) as MiRemoteUser | undefined;
+		if (actor && actor.isSuspended) {
 			throw new IdentifiableError('85ab9bd7-3a41-4530-959d-f07073900109', 'actor has been suspended');
 		}
 
@@ -189,7 +208,8 @@ export class ApNoteService {
 		}
 		//#endregion
 
-		const actor = cachedActor ?? await this.apPersonService.resolvePerson(uri, resolver) as MiRemoteUser;
+		// eslint-disable-next-line no-param-reassign
+		actor ??= await this.apPersonService.resolvePerson(uri, resolver) as MiRemoteUser;
 
 		// 解決した投稿者が凍結されていたらスキップ
 		if (actor.isSuspended) {
@@ -348,7 +368,7 @@ export class ApNoteService {
 			if (exist) return exist;
 			//#endregion
 
-			if (uri.startsWith(this.config.url)) {
+			if (this.utilityService.isUriLocal(uri)) {
 				throw new StatusError('cannot resolve local note', 400, 'cannot resolve local note');
 			}
 
@@ -356,7 +376,7 @@ export class ApNoteService {
 			// ここでuriの代わりに添付されてきたNote Objectが指定されていると、サーバーフェッチを経ずにノートが生成されるが
 			// 添付されてきたNote Objectは偽装されている可能性があるため、常にuriを指定してサーバーフェッチを行う。
 			const createFrom = options.sentFrom?.origin === new URL(uri).origin ? value : uri;
-			return await this.createNote(createFrom, options.resolver, true);
+			return await this.createNote(createFrom, undefined, options.resolver, true);
 		} finally {
 			unlock();
 		}
diff --git a/packages/backend/src/core/activitypub/models/ApPersonService.ts b/packages/backend/src/core/activitypub/models/ApPersonService.ts
index 8c4e40c561..026ddb6ece 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -129,12 +129,6 @@ export class ApPersonService implements OnModuleInit {
 		this.logger = this.apLoggerService.logger;
 	}
 
-	private punyHost(url: string): string {
-		const urlObj = new URL(url);
-		const host = `${this.utilityService.toPuny(urlObj.hostname)}${urlObj.port.length > 0 ? ':' + urlObj.port : ''}`;
-		return host;
-	}
-
 	/**
 	 * Validate and convert to actor object
 	 * @param x Fetched object
@@ -142,7 +136,7 @@ export class ApPersonService implements OnModuleInit {
 	 */
 	@bindThis
 	private validateActor(x: IObject, uri: string): IActor {
-		const expectHost = this.punyHost(uri);
+		const expectHost = this.utilityService.punyHost(uri);
 
 		if (!isActor(x)) {
 			throw new Error(`invalid Actor type '${x.type}'`);
@@ -156,6 +150,29 @@ export class ApPersonService implements OnModuleInit {
 			throw new Error('invalid Actor: wrong inbox');
 		}
 
+		if (this.utilityService.punyHost(x.inbox) !== expectHost) {
+			throw new Error('invalid Actor: inbox has different host');
+		}
+
+		const sharedInboxObject = x.sharedInbox ?? (x.endpoints ? x.endpoints.sharedInbox : undefined);
+		if (sharedInboxObject != null) {
+			const sharedInbox = getApId(sharedInboxObject);
+			if (!(typeof sharedInbox === 'string' && sharedInbox.length > 0 && this.utilityService.punyHost(sharedInbox) === expectHost)) {
+				throw new Error('invalid Actor: wrong shared inbox');
+			}
+		}
+
+		for (const collection of ['outbox', 'followers', 'following'] as (keyof IActor)[]) {
+			const collectionUri = getApId((x as IActor)[collection]);
+			if (typeof collectionUri === 'string' && collectionUri.length > 0) {
+				if (this.utilityService.punyHost(collectionUri) !== expectHost) {
+					throw new Error(`invalid Actor: ${collection} has different host`);
+				}
+			} else if (collectionUri != null) {
+				throw new Error(`invalid Actor: wrong ${collection}`);
+			}
+		}
+
 		if (!(typeof x.preferredUsername === 'string' && x.preferredUsername.length > 0 && x.preferredUsername.length <= 128 && /^\w([\w-.]*\w)?$/.test(x.preferredUsername))) {
 			throw new Error('invalid Actor: wrong username');
 		}
@@ -179,7 +196,7 @@ export class ApPersonService implements OnModuleInit {
 			x.summary = truncate(x.summary, summaryLength);
 		}
 
-		const idHost = this.punyHost(x.id);
+		const idHost = this.utilityService.punyHost(x.id);
 		if (idHost !== expectHost) {
 			throw new Error('invalid Actor: id has different host');
 		}
@@ -189,7 +206,7 @@ export class ApPersonService implements OnModuleInit {
 				throw new Error('invalid Actor: publicKey.id is not a string');
 			}
 
-			const publicKeyIdHost = this.punyHost(x.publicKey.id);
+			const publicKeyIdHost = this.utilityService.punyHost(x.publicKey.id);
 			if (publicKeyIdHost !== expectHost) {
 				throw new Error('invalid Actor: publicKey.id has different host');
 			}
@@ -280,7 +297,8 @@ export class ApPersonService implements OnModuleInit {
 	public async createPerson(uri: string, resolver?: Resolver): Promise<MiRemoteUser> {
 		if (typeof uri !== 'string') throw new Error('uri is not string');
 
-		if (uri.startsWith(this.config.url)) {
+		const host = this.utilityService.punyHost(uri);
+		if (host === this.utilityService.toPuny(this.config.host)) {
 			throw new StatusError('cannot resolve local user', 400, 'cannot resolve local user');
 		}
 
@@ -294,8 +312,6 @@ export class ApPersonService implements OnModuleInit {
 
 		this.logger.info(`Creating the Person: ${person.id}`);
 
-		const host = this.punyHost(object.id);
-
 		const fields = this.analyzeAttachments(person.attachment ?? []);
 
 		const tags = extractApHashtags(person.tag).map(normalizeForSearch).splice(0, 32);
@@ -321,8 +337,18 @@ export class ApPersonService implements OnModuleInit {
 
 		const url = getOneApHrefNullable(person.url);
 
-		if (url && !checkHttps(url)) {
-			throw new Error('unexpected schema of person url: ' + url);
+		if (person.id == null) {
+			throw new Error('Refusing to create person without id');
+		}
+
+		if (url != null) {
+			if (!checkHttps(url)) {
+				throw new Error('unexpected schema of person url: ' + url);
+			}
+
+			if (this.utilityService.punyHost(url) !== this.utilityService.punyHost(person.id)) {
+				throw new Error(`person url <> uri host mismatch: ${url} <> ${person.id}`);
+			}
 		}
 
 		// Create user
@@ -465,7 +491,7 @@ export class ApPersonService implements OnModuleInit {
 		if (typeof uri !== 'string') throw new Error('uri is not string');
 
 		// URIがこのサーバーを指しているならスキップ
-		if (uri.startsWith(`${this.config.url}/`)) return;
+		if (this.utilityService.isUriLocal(uri)) return;
 
 		//#region このサーバーに既に登録されているか
 		const exist = await this.fetchPerson(uri) as MiRemoteUser | null;
@@ -514,8 +540,18 @@ export class ApPersonService implements OnModuleInit {
 
 		const url = getOneApHrefNullable(person.url);
 
-		if (url && !checkHttps(url)) {
-			throw new Error('unexpected schema of person url: ' + url);
+		if (person.id == null) {
+			throw new Error('Refusing to update person without id');
+		}
+
+		if (url != null) {
+			if (!checkHttps(url)) {
+				throw new Error('unexpected schema of person url: ' + url);
+			}
+
+			if (this.utilityService.punyHost(url) !== this.utilityService.punyHost(person.id)) {
+				throw new Error(`person url <> uri host mismatch: ${url} <> ${person.id}`);
+			}
 		}
 
 		const updates = {
@@ -728,7 +764,7 @@ export class ApPersonService implements OnModuleInit {
 			await this.updatePerson(src.movedToUri, undefined, undefined, [...movePreventUris, src.uri]);
 			dst = await this.fetchPerson(src.movedToUri) ?? dst;
 		} else {
-			if (src.movedToUri.startsWith(`${this.config.url}/`)) {
+			if (this.utilityService.isUriLocal(src.movedToUri)) {
 				// ローカルユーザーっぽいのにfetchPersonで見つからないということはmovedToUriが間違っている
 				return 'failed: movedTo is local but not found';
 			}
diff --git a/packages/backend/src/core/activitypub/models/ApQuestionService.ts b/packages/backend/src/core/activitypub/models/ApQuestionService.ts
index 73004d10b0..1655a307c4 100644
--- a/packages/backend/src/core/activitypub/models/ApQuestionService.ts
+++ b/packages/backend/src/core/activitypub/models/ApQuestionService.ts
@@ -10,6 +10,7 @@ import type { Config } from '@/config.js';
 import type { IPoll } from '@/models/Poll.js';
 import type Logger from '@/logger.js';
 import { bindThis } from '@/decorators.js';
+import { UtilityService } from '@/core/UtilityService.js';
 import { isQuestion } from '../type.js';
 import { ApLoggerService } from '../ApLoggerService.js';
 import { ApResolverService } from '../ApResolverService.js';
@@ -32,6 +33,7 @@ export class ApQuestionService {
 
 		private apResolverService: ApResolverService,
 		private apLoggerService: ApLoggerService,
+		private utilityService: UtilityService,
 	) {
 		this.logger = this.apLoggerService.logger;
 	}
@@ -70,7 +72,7 @@ export class ApQuestionService {
 		if (uri == null) throw new Error('uri is null');
 
 		// URIがこのサーバーを指しているならスキップ
-		if (uri.startsWith(this.config.url + '/')) throw new Error('uri points local');
+		if (this.utilityService.isUriLocal(uri)) throw new Error('uri points local');
 
 		//#region このサーバーに既に登録されているか
 		const note = await this.notesRepository.findOneBy({ uri });
diff --git a/packages/backend/src/queue/processors/InboxProcessorService.ts b/packages/backend/src/queue/processors/InboxProcessorService.ts
index 95d764e4d8..004fe1382d 100644
--- a/packages/backend/src/queue/processors/InboxProcessorService.ts
+++ b/packages/backend/src/queue/processors/InboxProcessorService.ts
@@ -190,6 +190,8 @@ export class InboxProcessorService implements OnApplicationShutdown {
 			if (signerHost !== activityIdHost) {
 				throw new Bull.UnrecoverableError(`skip: signerHost(${signerHost}) !== activity.id host(${activityIdHost}`);
 			}
+		} else {
+			throw new Bull.UnrecoverableError('skip: activity id is not a string');
 		}
 
 		this.apRequestChart.inbox();
diff --git a/packages/backend/src/server/ActivityPubServerService.ts b/packages/backend/src/server/ActivityPubServerService.ts
index ba2342b630..f34f6583d3 100644
--- a/packages/backend/src/server/ActivityPubServerService.ts
+++ b/packages/backend/src/server/ActivityPubServerService.ts
@@ -105,7 +105,7 @@ export class ActivityPubServerService {
 		let signature;
 
 		try {
-			signature = httpSignature.parseRequest(request.raw, { 'headers': [] });
+			signature = httpSignature.parseRequest(request.raw, { 'headers': ['(request-target)', 'host', 'date'], authorizationHeaderName: 'signature' });
 		} catch (e) {
 			reply.code(401);
 			return;
diff --git a/packages/backend/src/server/api/endpoints/ap/get.ts b/packages/backend/src/server/api/endpoints/ap/get.ts
index d8c55de7ec..14286bc23e 100644
--- a/packages/backend/src/server/api/endpoints/ap/get.ts
+++ b/packages/backend/src/server/api/endpoints/ap/get.ts
@@ -11,6 +11,7 @@ import { ApResolverService } from '@/core/activitypub/ApResolverService.js';
 export const meta = {
 	tags: ['federation'],
 
+	requireAdmin: true,
 	requireCredential: true,
 	kind: 'read:federation',
 
diff --git a/packages/backend/src/server/api/endpoints/ap/show.ts b/packages/backend/src/server/api/endpoints/ap/show.ts
index c52608cefb..aca8258c08 100644
--- a/packages/backend/src/server/api/endpoints/ap/show.ts
+++ b/packages/backend/src/server/api/endpoints/ap/show.ts
@@ -118,6 +118,11 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 		]));
 		if (local != null) return local;
 
+		const host = this.utilityService.extractDbHost(uri);
+
+		// local object, not found in db? fail
+		if (this.utilityService.isSelfHost(host)) return null;
+
 		// リモートから一旦オブジェクトフェッチ
 		const resolver = this.apResolverService.createResolver();
 		const object = await resolver.resolve(uri) as any;