diff --git a/packages/backend/src/core/HttpRequestService.ts b/packages/backend/src/core/HttpRequestService.ts
index 3eb2a8089..4c1accae4 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 38f45a03a..40cb41343 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 16c71e971..7d3a74cf5 100644
--- a/packages/backend/src/core/UtilityService.ts
+++ b/packages/backend/src/core/UtilityService.ts
@@ -30,6 +30,11 @@ export class UtilityService {
 		return this.toPuny(this.config.host) === this.toPuny(host);
 	}
 
+	@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;
@@ -90,7 +95,7 @@ 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
@@ -103,4 +108,11 @@ export class UtilityService {
 		if (host == null) return null;
 		return punycode.toASCII(host.toLowerCase());
 	}
+
+	@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;
+	}
 }
diff --git a/packages/backend/src/core/activitypub/ApDbResolverService.ts b/packages/backend/src/core/activitypub/ApDbResolverService.ts
index 4192e8659..5c16744a7 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 0b6de71ea..568113a9b 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -90,15 +90,26 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	public async performActivity(actor: MiRemoteUser, activity: IObject, additionalCc?: MiLocalUser['id']): Promise<string> {
+	public async performActivity(actor: MiRemoteUser, activity: IObject, resolver?: Resolver, additionalCc?: MiLocalUser['id']): Promise<string> {
 		let result = 'error';
 		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: ${this.utilityService.extractDbHost(actor.uri)}`);
+			}
+
+			for (const item of items) {
 				const act = await resolver.resolve(item);
+				if (act.id == null || this.utilityService.extractDbHost(act.id) !== this.utilityService.extractDbHost(actor.uri)) {
+					this.logger.warn('skipping activity: activity id is null or mismatching');
+					continue;
+				}
 				try {
-					results.push([getApId(item), await this.performOneActivity(actor, act, additionalCc)]);
+					results.push([getApId(item), await this.performOneActivity(actor, act, resolver, additionalCc)]);
 				} catch (err) {
 					if (err instanceof Error || typeof err === 'string') {
 						this.logger.error(err);
@@ -113,7 +124,7 @@ export class ApInboxService {
 				result = results.map(([id, reason]) => `${id}: ${reason}`).join('\n');
 			}
 		} else {
-			result = await this.performOneActivity(actor, activity, additionalCc);
+			result = await this.performOneActivity(actor, activity, resolver, additionalCc);
 		}
 
 		// 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
@@ -129,37 +140,37 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	public async performOneActivity(actor: MiRemoteUser, activity: IObject, additionalCc?: MiLocalUser['id']): Promise<string> {
+	public async performOneActivity(actor: MiRemoteUser, activity: IObject, resolver?: Resolver, additionalCc?: MiLocalUser['id']): Promise<string> {
 		if (actor.isSuspended) return 'skip: actor is suspended';
 
 		if (isCreate(activity)) {
-			return await this.create(actor, activity, additionalCc);
+			return await this.create(actor, activity, resolver, additionalCc);
 		} else if (isDelete(activity)) {
 			return await this.delete(actor, activity);
 		} else if (isUpdate(activity)) {
-			return await this.update(actor, activity, additionalCc);
+			return await this.update(actor, activity, resolver, additionalCc);
 		} 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).catch(err => { this.logger.error(err); return `error: ${err.message}`; });
+			return await this.add(actor, activity, resolver).catch(err => { this.logger.error(err); return `error: ${err.message}`; });
 		} else if (isRemove(activity)) {
-			return await this.remove(actor, activity).catch(err => { this.logger.error(err); return `error: ${err.message}`; });
+			return await this.remove(actor, activity, resolver).catch(err => { this.logger.error(err); return `error: ${err.message}`; });
 		} 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 `skip: unknown activity type ${activity.type}`;
 		}
@@ -201,12 +212,13 @@ 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}`, { error: err });
@@ -243,7 +255,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async add(actor: MiRemoteUser, activity: IAdd): Promise<string> {
+	private async add(actor: MiRemoteUser, activity: IAdd, resolver?: Resolver): Promise<string> {
 		if (actor.uri !== activity.actor) {
 			return 'skip: invalid actor';
 		}
@@ -253,7 +265,7 @@ 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 'skip: note not found';
 			await this.notePiningService.addPinned(actor, note.id);
 			return 'ok';
@@ -263,12 +275,13 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async announce(actor: MiRemoteUser, activity: IAnnounce): Promise<string> {
+	private async announce(actor: MiRemoteUser, activity: IAnnounce, resolver?: Resolver): Promise<string> {
 		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';
 
@@ -283,7 +296,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async announceNote(actor: MiRemoteUser, activity: IAnnounce, target: IPost): Promise<string> {
+	private async announceNote(actor: MiRemoteUser, activity: IAnnounce, target: IPost, resolver?: Resolver): Promise<string> {
 		const uri = getApId(activity);
 
 		if (actor.isSuspended) {
@@ -306,7 +319,7 @@ 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 'skip: target note not found';
 			} catch (err) {
 				// 対象が4xxならスキップ
@@ -326,7 +339,7 @@ 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) {
@@ -366,7 +379,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async create(actor: MiRemoteUser, activity: ICreate, additionalCc?: MiLocalUser['id']): Promise<string> {
+	private async create(actor: MiRemoteUser, activity: ICreate, resolver?: Resolver, additionalCc?: MiLocalUser['id']): Promise<string> {
 		const uri = getApId(activity);
 
 		this.logger.info(`Create: ${uri}`);
@@ -389,7 +402,8 @@ 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}`, { error: e });
@@ -416,6 +430,8 @@ 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';
 			}
 		}
 
@@ -431,7 +447,7 @@ export class ApInboxService {
 				return 'skip: note exists';
 			}
 
-			const createdNote = await this.apNoteService.createNote(note, resolver, silent);
+			const createdNote = await this.apNoteService.createNote(note, actor, resolver, silent);
 			if (createdNote && additionalCc && !await this.noteEntityService.isVisibleForMe(createdNote, additionalCc)) {
 				await this.noteCreateService.appendNoteVisibleUser(actor, createdNote, additionalCc);
 				return 'ok: note visible user appended';
@@ -572,12 +588,13 @@ 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}`, { error: e });
@@ -614,7 +631,7 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async remove(actor: MiRemoteUser, activity: IRemove): Promise<string> {
+	private async remove(actor: MiRemoteUser, activity: IRemove, resolver?: Resolver): Promise<string> {
 		if (actor.uri !== activity.actor) {
 			return 'skip: invalid actor';
 		}
@@ -624,7 +641,7 @@ 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 'skip: note not found';
 			await this.notePiningService.removePinned(actor, note.id);
 			return 'ok';
@@ -634,7 +651,7 @@ 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 'skip: invalid actor';
 		}
@@ -643,7 +660,8 @@ 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}`, { error: e });
@@ -767,14 +785,15 @@ export class ApInboxService {
 	}
 
 	@bindThis
-	private async update(actor: MiRemoteUser, activity: IUpdate, additionalCc?: MiLocalUser['id']): Promise<string> {
+	private async update(actor: MiRemoteUser, activity: IUpdate, resolver?: Resolver, additionalCc?: MiLocalUser['id']): 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}`, { error: e });
@@ -814,11 +833,11 @@ 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 fe58b42cf..f59fabba3 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,
 	) {
 		this.logger = this.loggerService.getLogger('ap:request');
 	}
@@ -216,7 +220,7 @@ export class ApRequestService {
 				const alternate = fragment.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);
 					}
 				}
@@ -227,7 +231,11 @@ 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 fbe32ba18..000f9d59f 100644
--- a/packages/backend/src/core/activitypub/ApResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApResolverService.ts
@@ -42,7 +42,7 @@ 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 {
 		return Array.from(this.history);
 	}
 
+	@bindThis
+	public getRecursionLimit(): number {
+		return this.recursionLimit;
+	}
+
 	@bindThis
 	public async resolveCollection(value: string | IObject): Promise<ICollection | IOrderedCollection> {
 		const collection = typeof value === 'string'
@@ -115,6 +120,18 @@ 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 000000000..78ba891a2
--- /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 60a14a4e7..bd00529da 100644
--- a/packages/backend/src/core/activitypub/models/ApNoteService.ts
+++ b/packages/backend/src/core/activitypub/models/ApNoteService.ts
@@ -80,7 +80,7 @@ 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);
 
@@ -101,6 +101,14 @@ 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;
 	}
 
@@ -118,7 +126,7 @@ 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();
 
@@ -127,7 +135,7 @@ export class ApNoteService {
 		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() },
@@ -142,14 +150,24 @@ 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}`);
@@ -162,8 +180,9 @@ 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', `User ${cachedActor.id} has been suspended.`);
 		}
 
@@ -195,7 +214,8 @@ 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) {
@@ -359,7 +379,7 @@ export class ApNoteService {
 			if (exist) return exist;
 			//#endregion
 
-			if (new URL(uri).origin === this.config.url) {
+			if (this.utilityService.isUriLocal(uri)) {
 				throw new StatusError('cannot resolve local note', 400, 'cannot resolve local note');
 			}
 
@@ -367,7 +387,7 @@ 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 cfb8d2797..634d3f25f 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -130,12 +130,6 @@ 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
@@ -143,7 +137,7 @@ 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}'`);
@@ -157,18 +151,26 @@ export class ApPersonService implements OnModuleInit {
 			throw new Error('invalid Actor: wrong inbox');
 		}
 
-		try {
-			new URL(x.inbox);
-		} catch {
-			throw new Error('invalid Actor: wrong inbox');
+		if (this.utilityService.punyHost(x.inbox) !== expectHost) {
+			throw new Error('invalid Actor: inbox has different host');
 		}
 
-		const sharedInbox = x.sharedInbox ?? x.endpoints?.sharedInbox;
-		if (typeof sharedInbox === 'string') {
-			try {
-				new URL(sharedInbox);
-			} catch {
-				throw new Error('invalid Actor: wrong sharedInbox');
+		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}`);
 			}
 		}
 
@@ -195,7 +197,7 @@ 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');
 		}
@@ -205,7 +207,7 @@ 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');
 			}
@@ -291,7 +293,8 @@ 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 (new URL(uri).origin === 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');
 		}
 
@@ -305,8 +308,6 @@ 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);
@@ -332,8 +333,18 @@ 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
@@ -470,7 +481,7 @@ 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 (new URL(uri).origin === 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;
@@ -519,8 +530,18 @@ 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 policy = await this.roleService.getUserPolicies(exist.id);
@@ -731,7 +752,7 @@ export class ApPersonService implements OnModuleInit {
 			await this.updatePerson(src.movedToUri, undefined, undefined, [...movePreventUris, src.uri]);
 			dst = await this.fetchPerson(src.movedToUri) ?? dst;
 		} else {
-			if (new URL(src.movedToUri).origin === 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 4e3df00e0..ce08d4098 100644
--- a/packages/backend/src/core/activitypub/models/ApQuestionService.ts
+++ b/packages/backend/src/core/activitypub/models/ApQuestionService.ts
@@ -11,6 +11,7 @@ import type { IPoll } from '@/models/Poll.js';
 import type Logger from '@/logger.js';
 import { bindThis } from '@/decorators.js';
 import { isNotNull } from '@/misc/is-not-null.js';
+import { UtilityService } from '@/core/UtilityService.js';
 import { isQuestion } from '../type.js';
 import { ApLoggerService } from '../ApLoggerService.js';
 import { ApResolverService } from '../ApResolverService.js';
@@ -33,6 +34,7 @@ export class ApQuestionService {
 
 		private apResolverService: ApResolverService,
 		private apLoggerService: ApLoggerService,
+		private utilityService: UtilityService,
 	) {
 		this.logger = this.apLoggerService.logger;
 	}
@@ -71,7 +73,7 @@ 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 (new URL(uri).origin === 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 0bb30d27f..1b11b167b 100644
--- a/packages/backend/src/queue/processors/InboxProcessorService.ts
+++ b/packages/backend/src/queue/processors/InboxProcessorService.ts
@@ -180,6 +180,8 @@ 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');
 		}
 
 		// Update stats
diff --git a/packages/backend/src/server/ActivityPubServerService.ts b/packages/backend/src/server/ActivityPubServerService.ts
index 8ba2daf79..0a6dc6370 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 d8c55de7e..14286bc23 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 d3c40dba5..7cfd398d4 100644
--- a/packages/backend/src/server/api/endpoints/ap/show.ts
+++ b/packages/backend/src/server/api/endpoints/ap/show.ts
@@ -122,6 +122,11 @@ 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;