diff --git a/packages/backend/src/boot/entry.ts b/packages/backend/src/boot/entry.ts
index afb48e526c..bbe6a57383 100644
--- a/packages/backend/src/boot/entry.ts
+++ b/packages/backend/src/boot/entry.ts
@@ -55,44 +55,42 @@ async function main() {
 	// Display detail of unhandled promise rejection
 	if (!envOption.quiet) {
 		process.on('unhandledRejection', e => {
-			try {
-				logger.error('Unhandled rejection:', inspect(e));
-			} catch {
-				console.error('Unhandled rejection:', inspect(e));
-			}
+			logger.error('Unhandled rejection:', inspect(e));
 		});
 	}
 
-	// Display detail of uncaught exception
-	process.on('uncaughtExceptionMonitor', ((err, origin) => {
-		try {
-			logger.error(`Uncaught exception (${origin}):`, err);
-		} catch {
-			console.error(`Uncaught exception (${origin}):`, err);
+	process.on('uncaughtException', (err) => {
+		// Workaround for https://github.com/node-fetch/node-fetch/issues/954
+		if (String(err).match(/^TypeError: .+ is an? url with embedded credentials.$/)) {
+			logger.debug('Suppressed node-fetch issue#954, but the current job may fail.');
+			return;
 		}
-	}));
+
+		// Workaround for https://github.com/node-fetch/node-fetch/issues/1845
+		if (String(err) === 'TypeError: Cannot read properties of undefined (reading \'body\')') {
+			logger.debug('Suppressed node-fetch issue#1845, but the current job may fail.');
+			return;
+		}
+
+		// Throw all other errors to avoid inconsistent state.
+		// (per NodeJS docs, it's unsafe to suppress arbitrary errors in an uncaughtException handler.)
+		throw err;
+	});
+
+	// Display detail of uncaught exception
+	process.on('uncaughtExceptionMonitor', (err, origin) => {
+		logger.error(`Uncaught exception (${origin}):`, err);
+	});
 
 	// Dying away...
 	process.on('disconnect', () => {
-		try {
-			logger.warn('IPC channel disconnected! The process may soon die.');
-		} catch {
-			console.warn('IPC channel disconnected! The process may soon die.');
-		}
+		logger.warn('IPC channel disconnected! The process may soon die.');
 	});
 	process.on('beforeExit', code => {
-		try {
-			logger.warn(`Event loop died! Process will exit with code ${code}.`);
-		} catch {
-			console.warn(`Event loop died! Process will exit with code ${code}.`);
-		}
+		logger.warn(`Event loop died! Process will exit with code ${code}.`);
 	});
 	process.on('exit', code => {
-		try {
-			logger.info(`The process is going to exit with code ${code}`);
-		} catch {
-			console.info(`The process is going to exit with code ${code}`);
-		}
+		logger.info(`The process is going to exit with code ${code}`);
 	});
 	//#endregion
 
diff --git a/packages/backend/src/core/CaptchaService.ts b/packages/backend/src/core/CaptchaService.ts
index c526a80aeb..020984a37f 100644
--- a/packages/backend/src/core/CaptchaService.ts
+++ b/packages/backend/src/core/CaptchaService.ts
@@ -9,7 +9,10 @@ import { bindThis } from '@/decorators.js';
 import { MetaService } from '@/core/MetaService.js';
 import { MiMeta } from '@/models/Meta.js';
 import Logger from '@/logger.js';
-import { LoggerService } from './LoggerService.js';
+import { LoggerService } from '@/core/LoggerService.js';
+import { CaptchaError } from '@/misc/captcha-error.js';
+
+export { CaptchaError } from '@/misc/captcha-error.js';
 
 export const supportedCaptchaProviders = ['none', 'hcaptcha', 'mcaptcha', 'recaptcha', 'turnstile', 'fc', 'testcaptcha'] as const;
 export type CaptchaProvider = typeof supportedCaptchaProviders[number];
@@ -49,18 +52,6 @@ export type CaptchaSetting = {
 	}
 };
 
-export class CaptchaError extends Error {
-	public readonly code: CaptchaErrorCode;
-	public readonly cause?: unknown;
-
-	constructor(code: CaptchaErrorCode, message: string, cause?: unknown) {
-		super(message, cause ? { cause } : undefined);
-		this.code = code;
-		this.cause = cause;
-		this.name = 'CaptchaError';
-	}
-}
-
 export type CaptchaSaveSuccess = {
 	success: true;
 };
diff --git a/packages/backend/src/core/DownloadService.ts b/packages/backend/src/core/DownloadService.ts
index cb5bdb6cb7..d1819f40a3 100644
--- a/packages/backend/src/core/DownloadService.ts
+++ b/packages/backend/src/core/DownloadService.ts
@@ -19,6 +19,7 @@ import type Logger from '@/logger.js';
 
 import { bindThis } from '@/decorators.js';
 import { renderInlineError } from '@/misc/render-inline-error.js';
+import { UtilityService } from '@/core/UtilityService.js';
 
 @Injectable()
 export class DownloadService {
@@ -30,6 +31,7 @@ export class DownloadService {
 
 		private httpRequestService: HttpRequestService,
 		private loggerService: LoggerService,
+		private readonly utilityService: UtilityService,
 	) {
 		this.logger = this.loggerService.getLogger('download');
 	}
@@ -38,6 +40,8 @@ export class DownloadService {
 	public async downloadUrl(url: string, path: string, options: { timeout?: number, operationTimeout?: number, maxSize?: number } = {} ): Promise<{
 		filename: string;
 	}> {
+		this.utilityService.assertUrl(url);
+
 		this.logger.debug(`Downloading ${chalk.cyan(url)} to ${chalk.cyanBright(path)} ...`);
 
 		const timeout = options.timeout ?? 30 * 1000;
diff --git a/packages/backend/src/core/HttpRequestService.ts b/packages/backend/src/core/HttpRequestService.ts
index 151097095d..bd72fefe4f 100644
--- a/packages/backend/src/core/HttpRequestService.ts
+++ b/packages/backend/src/core/HttpRequestService.ts
@@ -17,9 +17,9 @@ import { StatusError } from '@/misc/status-error.js';
 import { bindThis } from '@/decorators.js';
 import { validateContentTypeSetAsActivityPub } from '@/core/activitypub/misc/validator.js';
 import type { IObject, IObjectWithId } from '@/core/activitypub/type.js';
-import { ApUtilityService } from './activitypub/ApUtilityService.js';
+import { UtilityService } from '@/core/UtilityService.js';
+import { ApUtilityService } from '@/core/activitypub/ApUtilityService.js';
 import type { Response } from 'node-fetch';
-import type { URL } from 'node:url';
 import type { Socket } from 'node:net';
 
 export type HttpRequestSendOptions = {
@@ -27,7 +27,27 @@ export type HttpRequestSendOptions = {
 	validators?: ((res: Response) => void)[];
 };
 
-export function isPrivateIp(allowedPrivateNetworks: PrivateNetwork[] | undefined, ip: string, port?: number): boolean {
+export async function isPrivateUrl(url: URL, lookup: net.LookupFunction): Promise<boolean> {
+	const ip = await resolveIp(url, lookup);
+	return ip.range() !== 'unicast';
+}
+
+export async function resolveIp(url: URL, lookup: net.LookupFunction) {
+	if (ipaddr.isValid(url.hostname)) {
+		return ipaddr.parse(url.hostname);
+	}
+
+	const resolvedIp = await new Promise<string>((resolve, reject) => {
+		lookup(url.hostname, {}, (err, address) => {
+			if (err) reject(err);
+			else resolve(address as string);
+		});
+	});
+
+	return ipaddr.parse(resolvedIp);
+}
+
+export function isAllowedPrivateIp(allowedPrivateNetworks: PrivateNetwork[] | undefined, ip: string, port?: number): boolean {
 	const parsedIp = ipaddr.parse(ip);
 
 	for (const { cidr, ports } of allowedPrivateNetworks ?? []) {
@@ -44,7 +64,7 @@ export function isPrivateIp(allowedPrivateNetworks: PrivateNetwork[] | undefined
 export function validateSocketConnect(allowedPrivateNetworks: PrivateNetwork[] | undefined, socket: Socket): void {
 	const address = socket.remoteAddress;
 	if (address && ipaddr.isValid(address)) {
-		if (isPrivateIp(allowedPrivateNetworks, address, socket.remotePort)) {
+		if (isAllowedPrivateIp(allowedPrivateNetworks, address, socket.remotePort)) {
 			socket.destroy(new Error(`Blocked address: ${address}`));
 		}
 	}
@@ -128,10 +148,16 @@ export class HttpRequestService {
 	 */
 	public readonly httpsAgent: https.Agent;
 
+	/**
+	 * Get shared DNS resolver
+	 */
+	public readonly lookup: net.LookupFunction;
+
 	constructor(
 		@Inject(DI.config)
 		private config: Config,
 		private readonly apUtilityService: ApUtilityService,
+		private readonly utilityService: UtilityService,
 	) {
 		const cache = new CacheableLookup({
 			maxTtl: 3600,	// 1hours
@@ -139,6 +165,8 @@ export class HttpRequestService {
 			lookup: false,	// nativeのdns.lookupにfallbackしない
 		});
 
+		this.lookup = cache.lookup as unknown as net.LookupFunction;
+
 		const agentOption = {
 			keepAlive: true,
 			keepAliveMsecs: 30 * 1000,
@@ -236,8 +264,6 @@ export class HttpRequestService {
 
 	@bindThis
 	public async getActivityJson(url: string, isLocalAddressAllowed = false, allowAnonymous = false): Promise<IObjectWithId> {
-		this.apUtilityService.assertApUrl(url);
-
 		const res = await this.send(url, {
 			method: 'GET',
 			headers: {
@@ -303,6 +329,7 @@ export class HttpRequestService {
 			timeout?: number,
 			size?: number,
 			isLocalAddressAllowed?: boolean,
+			allowHttp?: boolean,
 		} = {},
 		extra: HttpRequestSendOptions = {
 			throwErrorWhenResponseNotOk: true,
@@ -311,6 +338,10 @@ export class HttpRequestService {
 	): Promise<Response> {
 		const timeout = args.timeout ?? 5000;
 
+		const parsedUrl = new URL(url);
+		const allowHttp = args.allowHttp || await isPrivateUrl(parsedUrl, this.lookup);
+		this.utilityService.assertUrl(parsedUrl, allowHttp);
+
 		const controller = new AbortController();
 		setTimeout(() => {
 			controller.abort();
@@ -318,7 +349,7 @@ export class HttpRequestService {
 
 		const isLocalAddressAllowed = args.isLocalAddressAllowed ?? false;
 
-		const res = await fetch(url, {
+		const res = await fetch(parsedUrl, {
 			method: args.method ?? 'GET',
 			headers: {
 				'User-Agent': this.config.userAgent,
diff --git a/packages/backend/src/core/UtilityService.ts b/packages/backend/src/core/UtilityService.ts
index 5de76e00a6..f4149f8037 100644
--- a/packages/backend/src/core/UtilityService.ts
+++ b/packages/backend/src/core/UtilityService.ts
@@ -11,8 +11,10 @@ import semver from 'semver';
 import { DI } from '@/di-symbols.js';
 import type { Config } from '@/config.js';
 import { bindThis } from '@/decorators.js';
-import { MiMeta, SoftwareSuspension } from '@/models/Meta.js';
-import { MiInstance } from '@/models/Instance.js';
+import type { MiMeta, SoftwareSuspension } from '@/models/Meta.js';
+import type { MiInstance } from '@/models/Instance.js';
+import { IdentifiableError } from '@/misc/identifiable-error.js';
+import { EnvService } from '@/core/EnvService.js';
 
 @Injectable()
 export class UtilityService {
@@ -22,6 +24,8 @@ export class UtilityService {
 
 		@Inject(DI.meta)
 		private meta: MiMeta,
+
+		private readonly envService: EnvService,
 	) {
 	}
 
@@ -183,8 +187,8 @@ export class UtilityService {
 	}
 
 	@bindThis
-	public punyHostPSLDomain(url: string): string {
-		const urlObj = new URL(url);
+	public punyHostPSLDomain(url: string | URL): string {
+		const urlObj = typeof(url) === 'object' ? url : new URL(url);
 		const hostname = urlObj.hostname;
 		const domain = this.specialSuffix(hostname) ?? psl.get(hostname) ?? hostname;
 		const host = `${this.toPuny(domain)}${urlObj.port.length > 0 ? ':' + urlObj.port : ''}`;
@@ -231,4 +235,52 @@ export class UtilityService {
 				&& semver.satisfies(softwareVersion, x.versionRange, { includePrerelease: true }));
 		}
 	}
+
+	/**
+	 * Verifies that a provided URL is in a format acceptable for federation.
+	 * @throws {IdentifiableError} If URL cannot be parsed
+	 * @throws {IdentifiableError} If URL is not HTTPS
+	 * @throws {IdentifiableError} If URL contains credentials
+	 */
+	@bindThis
+	public assertUrl(url: string | URL, allowHttp?: boolean): URL | never {
+		// If string, parse and validate
+		if (typeof(url) === 'string') {
+			try {
+				url = new URL(url);
+			} catch {
+				throw new IdentifiableError('0bedd29b-e3bf-4604-af51-d3352e2518af', `invalid url ${url}: not a valid URL`);
+			}
+		}
+
+		// Must be HTTPS
+		if (!this.checkHttps(url, allowHttp)) {
+			throw new IdentifiableError('0bedd29b-e3bf-4604-af51-d3352e2518af', `invalid url ${url}: unsupported protocol ${url.protocol}`);
+		}
+
+		// Must not have credentials
+		if (url.username || url.password) {
+			throw new IdentifiableError('0bedd29b-e3bf-4604-af51-d3352e2518af', `invalid url ${url}: contains embedded credentials`);
+		}
+
+		return url;
+	}
+
+	/**
+	 * Checks if the URL contains HTTPS.
+	 * Additionally, allows HTTP in non-production environments.
+	 * Based on check-https.ts.
+	 */
+	@bindThis
+	public checkHttps(url: string | URL, allowHttp = false): boolean {
+		const isNonProd = this.envService.env.NODE_ENV !== 'production';
+
+		try {
+			const proto = new URL(url).protocol;
+			return proto === 'https:' || (proto === 'http:' && (isNonProd || allowHttp));
+		} catch {
+			// Invalid URLs don't "count" as HTTPS
+			return false;
+		}
+	}
 }
diff --git a/packages/backend/src/core/activitypub/ApRequestService.ts b/packages/backend/src/core/activitypub/ApRequestService.ts
index e4db9b237c..7669ce9669 100644
--- a/packages/backend/src/core/activitypub/ApRequestService.ts
+++ b/packages/backend/src/core/activitypub/ApRequestService.ts
@@ -157,8 +157,6 @@ export class ApRequestService {
 
 	@bindThis
 	public async signedPost(user: { id: MiUser['id'] }, url: string, object: unknown, digest?: string): Promise<void> {
-		this.apUtilityService.assertApUrl(url);
-
 		const body = typeof object === 'string' ? object : JSON.stringify(object);
 
 		const keypair = await this.userKeypairService.getUserKeypair(user.id);
@@ -191,8 +189,6 @@ export class ApRequestService {
 	 */
 	@bindThis
 	public async signedGet(url: string, user: { id: MiUser['id'] }, allowAnonymous = false, followAlternate?: boolean): Promise<IObjectWithId> {
-		this.apUtilityService.assertApUrl(url);
-
 		const _followAlternate = followAlternate ?? true;
 		const keypair = await this.userKeypairService.getUserKeypair(user.id);
 
diff --git a/packages/backend/src/core/activitypub/ApUtilityService.ts b/packages/backend/src/core/activitypub/ApUtilityService.ts
index 227dc3b9b3..26ea0cd632 100644
--- a/packages/backend/src/core/activitypub/ApUtilityService.ts
+++ b/packages/backend/src/core/activitypub/ApUtilityService.ts
@@ -7,20 +7,29 @@ import { Injectable } from '@nestjs/common';
 import { UtilityService } from '@/core/UtilityService.js';
 import { IdentifiableError } from '@/misc/identifiable-error.js';
 import { toArray } from '@/misc/prelude/array.js';
-import { EnvService } from '@/core/EnvService.js';
-import { getApId, getOneApHrefNullable, IObject } from './type.js';
+import { getApId, getNullableApId, getOneApHrefNullable } from '@/core/activitypub/type.js';
+import type { IObject, IObjectWithId } from '@/core/activitypub/type.js';
+import { bindThis } from '@/decorators.js';
+import { renderInlineError } from '@/misc/render-inline-error.js';
+import { LoggerService } from '@/core/LoggerService.js';
+import type Logger from '@/logger.js';
 
 @Injectable()
 export class ApUtilityService {
+	private readonly logger: Logger;
+
 	constructor(
 		private readonly utilityService: UtilityService,
-		private readonly envService: EnvService,
-	) {}
+		loggerService: LoggerService,
+	) {
+		this.logger = loggerService.getLogger('ap-utility');
+	}
 
 	/**
 	 * Verifies that the object's ID has the same authority as the provided URL.
 	 * Returns on success, throws on any validation error.
 	 */
+	@bindThis
 	public assertIdMatchesUrlAuthority(object: IObject, url: string): void {
 		// This throws if the ID is missing or invalid, but that's ok.
 		// Anonymous objects are impossible to verify, so we don't allow fetching them.
@@ -36,11 +45,15 @@ export class ApUtilityService {
 	/**
 	 * Checks if two URLs have the same host authority
 	 */
+	@bindThis
 	public haveSameAuthority(url1: string, url2: string): boolean {
 		if (url1 === url2) return true;
 
-		const authority1 = this.utilityService.punyHostPSLDomain(url1);
-		const authority2 = this.utilityService.punyHostPSLDomain(url2);
+		const parsed1 = this.utilityService.assertUrl(url1);
+		const parsed2 = this.utilityService.assertUrl(url2);
+
+		const authority1 = this.utilityService.punyHostPSLDomain(parsed1);
+		const authority2 = this.utilityService.punyHostPSLDomain(parsed2);
 		return authority1 === authority2;
 	}
 
@@ -50,6 +63,7 @@ export class ApUtilityService {
 	 * @throws {IdentifiableError} if object does not have an ID
 	 * @returns the best URL, or null if none were found
 	 */
+	@bindThis
 	public findBestObjectUrl(object: IObject): string | null {
 		const targetUrl = getApId(object);
 		const targetAuthority = this.utilityService.punyHostPSLDomain(targetUrl);
@@ -63,12 +77,16 @@ export class ApUtilityService {
 					: undefined,
 			}))
 			.filter(({ url, type }) => {
-				if (!url) return false;
-				if (!this.checkHttps(url)) return false;
-				if (!isAcceptableUrlType(type)) return false;
+				try {
+					if (!url) return false;
+					if (!isAcceptableUrlType(type)) return false;
+					const parsed = this.utilityService.assertUrl(url);
 
-				const urlAuthority = this.utilityService.punyHostPSLDomain(url);
-				return urlAuthority === targetAuthority;
+					const urlAuthority = this.utilityService.punyHostPSLDomain(parsed);
+					return urlAuthority === targetAuthority;
+				} catch {
+					return false;
+				}
 			})
 			.sort((a, b) => {
 				return rankUrlType(a.type) - rankUrlType(b.type);
@@ -78,41 +96,72 @@ export class ApUtilityService {
 	}
 
 	/**
-	 * Verifies that a provided URL is in a format acceptable for federation.
-	 * @throws {IdentifiableError} If URL cannot be parsed
-	 * @throws {IdentifiableError} If URL is not HTTPS
+	 * Sanitizes an inline / nested Object property within an AP object.
+	 *
+	 * Returns true if the property contains a valid string URL, object w/ valid ID, or an array containing one of those.
+	 * Returns false and erases the property if it doesn't contain a valid value.
+	 *
+	 * Arrays are automatically flattened.
+	 * Falsy values (including null) are collapsed to undefined.
+	 * @param obj Object containing the property to validate
+	 * @param key Key of the property in obj
+	 * @param parentUri URI of the object that contains this inline object.
+	 * @param parentHost PSL host of parentUri
+	 * @param keyPath If obj is *itself* a nested object, set this to the property path from root to obj (including the trailing '.'). This does not affect the logic, but improves the clarity of logs.
 	 */
-	public assertApUrl(url: string | URL): void {
-		// If string, parse and validate
-		if (typeof(url) === 'string') {
-			try {
-				url = new URL(url);
-			} catch {
-				throw new IdentifiableError('0bedd29b-e3bf-4604-af51-d3352e2518af', `invalid AP url ${url}: not a valid URL`);
-			}
+	@bindThis
+	public sanitizeInlineObject<Key extends string>(obj: Partial<Record<Key, string | { id?: string } | (string | { id?: string })[]>>, key: Key, parentUri: string | URL, parentHost: string, keyPath = ''): obj is Partial<Record<Key, string | { id: string }>> {
+		let value: unknown = obj[key];
+
+		// Unpack arrays
+		if (Array.isArray(value)) {
+			value = value[0];
 		}
 
-		// Must be HTTPS
-		if (!this.checkHttps(url)) {
-			throw new IdentifiableError('0bedd29b-e3bf-4604-af51-d3352e2518af', `invalid AP url ${url}: unsupported protocol ${url.protocol}`);
-		}
-	}
+		// Clear the value - we'll add it back once we have a confirmed ID
+		obj[key] = undefined;
 
-	/**
-	 * Checks if the URL contains HTTPS.
-	 * Additionally, allows HTTP in non-production environments.
-	 * Based on check-https.ts.
-	 */
-	private checkHttps(url: string | URL): boolean {
-		const isNonProd = this.envService.env.NODE_ENV !== 'production';
-
-		try {
-			const proto = new URL(url).protocol;
-			return proto === 'https:' || (proto === 'http:' && isNonProd);
-		} catch {
-			// Invalid URLs don't "count" as HTTPS
+		// Collapse falsy values to undefined
+		if (!value) {
 			return false;
 		}
+
+		// Exclude nested arrays
+		if (Array.isArray(value)) {
+			this.logger.warn(`Excluding ${keyPath}${key} from object ${parentUri}: nested arrays are prohibited`);
+			return false;
+		}
+
+		// Exclude incorrect types
+		if (typeof(value) !== 'string' && typeof(value) !== 'object') {
+			this.logger.warn(`Excluding ${keyPath}${key} from object ${parentUri}: incorrect type ${typeof(value)}`);
+			return false;
+		}
+
+		const valueId = getNullableApId(value);
+		if (!valueId) {
+			// Exclude missing ID
+			this.logger.warn(`Excluding ${keyPath}${key} from object ${parentUri}: missing or invalid ID`);
+			return false;
+		}
+
+		try {
+			const parsed = this.utilityService.assertUrl(valueId);
+			const parsedHost = this.utilityService.punyHostPSLDomain(parsed);
+			if (parsedHost !== parentHost) {
+				// Exclude wrong host
+				this.logger.warn(`Excluding ${keyPath}${key} from object ${parentUri}: wrong host in ${valueId} (got ${parsedHost}, expected ${parentHost})`);
+				return false;
+			}
+		} catch (err) {
+			// Exclude invalid URLs
+			this.logger.warn(`Excluding ${keyPath}${key} from object ${parentUri}: invalid URL ${valueId}: ${renderInlineError(err)}`);
+			return false;
+		}
+
+		// Success - store the sanitized value and return
+		obj[key] = value as string | IObjectWithId;
+		return true;
 	}
 }
 
diff --git a/packages/backend/src/core/activitypub/models/ApNoteService.ts b/packages/backend/src/core/activitypub/models/ApNoteService.ts
index db26108fa2..32661fb6d9 100644
--- a/packages/backend/src/core/activitypub/models/ApNoteService.ts
+++ b/packages/backend/src/core/activitypub/models/ApNoteService.ts
@@ -100,7 +100,7 @@ export class ApNoteService {
 		actor?: MiRemoteUser,
 		user?: MiRemoteUser,
 	): Error | null {
-		this.apUtilityService.assertApUrl(uri);
+		this.utilityService.assertUrl(uri);
 		const expectHost = this.utilityService.extractDbHost(uri);
 		const apType = getApType(object);
 
diff --git a/packages/backend/src/core/activitypub/models/ApPersonService.ts b/packages/backend/src/core/activitypub/models/ApPersonService.ts
index a68a63099d..51b2375da0 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -153,89 +153,88 @@ export class ApPersonService implements OnModuleInit, OnApplicationShutdown {
 	 */
 	@bindThis
 	private validateActor(x: IObject, uri: string): IActor {
-		this.apUtilityService.assertApUrl(uri);
-		const expectHost = this.utilityService.punyHostPSLDomain(uri);
+		const parsedUri = this.utilityService.assertUrl(uri);
+		const expectHost = this.utilityService.punyHostPSLDomain(parsedUri);
 
+		// Validate type
 		if (!isActor(x)) {
 			throw new UnrecoverableError(`invalid Actor ${uri}: unknown type '${x.type}'`);
 		}
 
-		if (!(typeof x.id === 'string' && x.id.length > 0)) {
-			throw new UnrecoverableError(`invalid Actor ${uri}: wrong id type`);
+		// Validate id
+		if (!x.id) {
+			throw new UnrecoverableError(`invalid Actor ${uri}: missing id`);
+		}
+		if (typeof(x.id) !== 'string') {
+			throw new UnrecoverableError(`invalid Actor ${uri}: wrong id type ${typeof(x.id)}`);
+		}
+		const parsedId = this.utilityService.assertUrl(x.id);
+		const idHost = this.utilityService.punyHostPSLDomain(parsedId);
+		if (idHost !== expectHost) {
+			throw new UnrecoverableError(`invalid Actor ${uri}: wrong host in id ${x.id} (got ${parsedId}, expected ${expectHost})`);
 		}
 
-		if (!(typeof x.inbox === 'string' && x.inbox.length > 0)) {
-			throw new UnrecoverableError(`invalid Actor ${uri}: wrong inbox type`);
+		// Validate inbox
+		this.apUtilityService.sanitizeInlineObject(x, 'inbox', parsedUri, expectHost);
+		if (!x.inbox || typeof(x.inbox) !== 'string') {
+			throw new UnrecoverableError(`invalid Actor ${uri}: missing or invalid inbox ${x.inbox}`);
 		}
 
-		this.apUtilityService.assertApUrl(x.inbox);
-		const inboxHost = this.utilityService.punyHostPSLDomain(x.inbox);
-		if (inboxHost !== expectHost) {
-			throw new UnrecoverableError(`invalid Actor ${uri}: wrong inbox host ${inboxHost}`);
+		// Sanitize sharedInbox
+		this.apUtilityService.sanitizeInlineObject(x, 'sharedInbox', parsedUri, expectHost);
+
+		// Sanitize endpoints object
+		if (typeof(x.endpoints) === 'object') {
+			x.endpoints = {
+				sharedInbox: x.endpoints.sharedInbox,
+			};
+		} else {
+			x.endpoints = undefined;
 		}
 
-		const sharedInboxObject = x.sharedInbox ?? (x.endpoints ? x.endpoints.sharedInbox : undefined);
-		if (sharedInboxObject != null) {
-			const sharedInbox = getApId(sharedInboxObject);
-			this.apUtilityService.assertApUrl(sharedInbox);
-			if (!(typeof sharedInbox === 'string' && sharedInbox.length > 0 && this.utilityService.punyHostPSLDomain(sharedInbox) === expectHost)) {
-				throw new UnrecoverableError(`invalid Actor ${uri}: wrong shared inbox ${sharedInbox}`);
+		// Sanitize endpoints.sharedInbox
+		if (x.endpoints) {
+			this.apUtilityService.sanitizeInlineObject(x.endpoints, 'sharedInbox', parsedUri, expectHost, 'endpoints.');
+
+			if (!x.endpoints.sharedInbox) {
+				x.endpoints = undefined;
 			}
 		}
 
-		for (const collection of ['outbox', 'followers', 'following'] as (keyof IActor)[]) {
-			const xCollection = (x as IActor)[collection];
-			if (xCollection != null) {
-				const collectionUri = getApId(xCollection);
-				if (typeof collectionUri === 'string' && collectionUri.length > 0) {
-					this.apUtilityService.assertApUrl(collectionUri);
-					if (this.utilityService.punyHostPSLDomain(collectionUri) !== expectHost) {
-						throw new UnrecoverableError(`invalid Actor ${uri}: wrong ${collection} host ${collectionUri}`);
-					}
-				} else if (collectionUri != null) {
-					throw new UnrecoverableError(`invalid Actor ${uri}: wrong ${collection} type`);
-				}
-			}
+		// Sanitize collections
+		for (const collection of ['outbox', 'followers', 'following', 'featured'] as const) {
+			this.apUtilityService.sanitizeInlineObject(x, collection, parsedUri, expectHost);
 		}
 
+		// Validate username
 		if (!(typeof x.preferredUsername === 'string' && x.preferredUsername.length > 0 && x.preferredUsername.length <= 128 && /^\w([\w-.]*\w)?$/.test(x.preferredUsername))) {
 			throw new UnrecoverableError(`invalid Actor ${uri}: wrong username`);
 		}
 
+		// Sanitize name
 		// These fields are only informational, and some AP software allows these
 		// fields to be very long. If they are too long, we cut them off. This way
 		// we can at least see these users and their activities.
-		if (x.name) {
-			if (!(typeof x.name === 'string' && x.name.length > 0)) {
-				throw new UnrecoverableError(`invalid Actor ${uri}: wrong name`);
-			}
-			x.name = truncate(x.name, nameLength);
-		} else if (x.name === '') {
-			// Mastodon emits empty string when the name is not set.
+		if (!x.name) {
 			x.name = undefined;
+		} else if (typeof(x.name) !== 'string') {
+			this.logger.warn(`Excluding name from object ${uri}: incorrect type ${typeof(x)}`);
+			x.name = undefined;
+		} else {
+			x.name = truncate(x.name, nameLength);
 		}
-		if (x.summary) {
-			if (!(typeof x.summary === 'string' && x.summary.length > 0)) {
-				throw new UnrecoverableError(`invalid Actor ${uri}: wrong summary`);
-			}
+
+		// Sanitize summary
+		if (!x.summary) {
+			x.summary = undefined;
+		} else if (typeof(x.summary) !== 'string') {
+			this.logger.warn(`Excluding summary from object ${uri}: incorrect type ${typeof(x)}`);
+		} else {
 			x.summary = truncate(x.summary, this.config.maxRemoteBioLength);
 		}
 
-		const idHost = this.utilityService.punyHostPSLDomain(x.id);
-		if (idHost !== expectHost) {
-			throw new UnrecoverableError(`invalid Actor ${uri}: wrong id ${x.id}`);
-		}
-
-		if (x.publicKey) {
-			if (typeof x.publicKey.id !== 'string') {
-				throw new UnrecoverableError(`invalid Actor ${uri}: wrong publicKey.id type`);
-			}
-
-			const publicKeyIdHost = this.utilityService.punyHostPSLDomain(x.publicKey.id);
-			if (publicKeyIdHost !== expectHost) {
-				throw new UnrecoverableError(`invalid Actor ${uri}: wrong publicKey.id ${x.publicKey.id}`);
-			}
-		}
+		// Sanitize publicKey
+		this.apUtilityService.sanitizeInlineObject(x, 'publicKey', parsedUri, expectHost);
 
 		return x;
 	}
diff --git a/packages/backend/src/core/activitypub/type.ts b/packages/backend/src/core/activitypub/type.ts
index 5d4b2b01c5..e86495c03e 100644
--- a/packages/backend/src/core/activitypub/type.ts
+++ b/packages/backend/src/core/activitypub/type.ts
@@ -86,7 +86,7 @@ export function getOneApId(value: ApObject): string {
 /**
  * Get ActivityStreams Object id
  */
-export function getApId(value: string | IObject | [string | IObject], sourceForLogs?: string): string {
+export function getApId(value: unknown | [unknown] | unknown[], sourceForLogs?: string): string {
 	const id = getNullableApId(value);
 
 	if (id == null) {
@@ -102,7 +102,7 @@ export function getApId(value: string | IObject | [string | IObject], sourceForL
 /**
  * Get ActivityStreams Object id, or null if not present
  */
-export function getNullableApId(source: string | IObject | [string | IObject]): string | null {
+export function getNullableApId(source: unknown | [unknown] | unknown[]): string | null {
 	const value: unknown = fromTuple(source);
 
 	if (value != null) {
@@ -276,7 +276,7 @@ export interface IActor extends IObject {
 	followers?: string | ICollection | IOrderedCollection;
 	following?: string | ICollection | IOrderedCollection;
 	featured?: string | IOrderedCollection;
-	outbox: string | IOrderedCollection;
+	outbox?: string | IOrderedCollection;
 	endpoints?: {
 		sharedInbox?: string;
 	};
diff --git a/packages/backend/src/misc/captcha-error.ts b/packages/backend/src/misc/captcha-error.ts
new file mode 100644
index 0000000000..217018ec68
--- /dev/null
+++ b/packages/backend/src/misc/captcha-error.ts
@@ -0,0 +1,18 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { CaptchaErrorCode } from '@/core/CaptchaService.js';
+
+export class CaptchaError extends Error {
+	public readonly code: CaptchaErrorCode;
+	public readonly cause?: unknown;
+
+	constructor(code: CaptchaErrorCode, message: string, cause?: unknown) {
+		super(message, cause ? { cause } : undefined);
+		this.code = code;
+		this.cause = cause;
+		this.name = 'CaptchaError';
+	}
+}
diff --git a/packages/backend/src/misc/render-inline-error.ts b/packages/backend/src/misc/render-inline-error.ts
index 07f9f3068e..886efcb86e 100644
--- a/packages/backend/src/misc/render-inline-error.ts
+++ b/packages/backend/src/misc/render-inline-error.ts
@@ -5,7 +5,7 @@
 
 import { IdentifiableError } from '@/misc/identifiable-error.js';
 import { StatusError } from '@/misc/status-error.js';
-import { CaptchaError } from '@/core/CaptchaService.js';
+import { CaptchaError } from '@/misc/captcha-error.js';
 
 export function renderInlineError(err: unknown): string {
 	const parts: string[] = [];
diff --git a/packages/backend/src/misc/verify-field-link.ts b/packages/backend/src/misc/verify-field-link.ts
index 6a3c950059..31a356be37 100644
--- a/packages/backend/src/misc/verify-field-link.ts
+++ b/packages/backend/src/misc/verify-field-link.ts
@@ -10,8 +10,9 @@ type Field = { name: string, value: string };
 
 export async function verifyFieldLinks(fields: Field[], profileUrls: string[], httpRequestService: HttpRequestService): Promise<string[]> {
 	const verified_links = [];
-	for (const field_url of fields.filter(x => URL.canParse(x.value) && ['http:', 'https:'].includes((new URL(x.value).protocol)))) {
+	for (const field_url of fields) {
 		try {
+			// getHtml validates the input URL, so we can safely pass in untrusted values
 			const html = await httpRequestService.getHtml(field_url.value);
 
 			const doc = cheerio(html);
diff --git a/packages/backend/test/unit/FetchInstanceMetadataService.ts b/packages/backend/test/unit/FetchInstanceMetadataService.ts
index 1e3605aafc..812ee38703 100644
--- a/packages/backend/test/unit/FetchInstanceMetadataService.ts
+++ b/packages/backend/test/unit/FetchInstanceMetadataService.ts
@@ -16,6 +16,7 @@ import { HttpRequestService } from '@/core/HttpRequestService.js';
 import { LoggerService } from '@/core/LoggerService.js';
 import { UtilityService } from '@/core/UtilityService.js';
 import { IdService } from '@/core/IdService.js';
+import { EnvService } from '@/core/EnvService.js';
 import { DI } from '@/di-symbols.js';
 
 function mockRedis() {
@@ -46,6 +47,7 @@ describe('FetchInstanceMetadataService', () => {
 					LoggerService,
 					UtilityService,
 					IdService,
+					EnvService,
 				],
 			})
 			.useMocker((token) => {
diff --git a/packages/backend/test/unit/core/HttpRequestService.ts b/packages/backend/test/unit/core/HttpRequestService.ts
index a2f4604e7b..ccce32ffee 100644
--- a/packages/backend/test/unit/core/HttpRequestService.ts
+++ b/packages/backend/test/unit/core/HttpRequestService.ts
@@ -3,11 +3,11 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { jest } from '@jest/globals';
+import { describe, jest } from '@jest/globals';
 import type { Mock } from 'jest-mock';
 import type { PrivateNetwork } from '@/config.js';
 import type { Socket } from 'net';
-import { HttpRequestService, isPrivateIp, validateSocketConnect } from '@/core/HttpRequestService.js';
+import { HttpRequestService, isAllowedPrivateIp, isPrivateUrl, resolveIp, validateSocketConnect } from '@/core/HttpRequestService.js';
 import { parsePrivateNetworks } from '@/config.js';
 
 describe(HttpRequestService, () => {
@@ -21,38 +21,85 @@ describe(HttpRequestService, () => {
 		]);
 	});
 
-	describe('isPrivateIp', () => {
+	describe(isAllowedPrivateIp, () => {
 		it('should return false when ip public', () => {
-			const result = isPrivateIp(allowedPrivateNetworks, '74.125.127.100', 80);
+			const result = isAllowedPrivateIp(allowedPrivateNetworks, '74.125.127.100', 80);
 			expect(result).toBeFalsy();
 		});
 
 		it('should return false when ip private and port matches', () => {
-			const result = isPrivateIp(allowedPrivateNetworks, '127.0.0.1', 1);
+			const result = isAllowedPrivateIp(allowedPrivateNetworks, '127.0.0.1', 1);
 			expect(result).toBeFalsy();
 		});
 
 		it('should return false when ip private and all ports undefined', () => {
-			const result = isPrivateIp(allowedPrivateNetworks, '10.0.0.1', undefined);
+			const result = isAllowedPrivateIp(allowedPrivateNetworks, '10.0.0.1', undefined);
 			expect(result).toBeFalsy();
 		});
 
 		it('should return true when ip private and no ports specified', () => {
-			const result = isPrivateIp(allowedPrivateNetworks, '10.0.0.2', 80);
+			const result = isAllowedPrivateIp(allowedPrivateNetworks, '10.0.0.2', 80);
 			expect(result).toBeTruthy();
 		});
 
 		it('should return true when ip private and port does not match', () => {
-			const result = isPrivateIp(allowedPrivateNetworks, '127.0.0.1', 80);
+			const result = isAllowedPrivateIp(allowedPrivateNetworks, '127.0.0.1', 80);
 			expect(result).toBeTruthy();
 		});
 
 		it('should return true when ip private and port is null but ports are specified', () => {
-			const result = isPrivateIp(allowedPrivateNetworks, '127.0.0.1', undefined);
+			const result = isAllowedPrivateIp(allowedPrivateNetworks, '127.0.0.1', undefined);
 			expect(result).toBeTruthy();
 		});
 	});
 
+	const fakeLookup = (host: string, _: unknown, callback: (err: Error | null, ip: string) => void) => {
+		if (host === 'localhost') {
+			callback(null, '127.0.0.1');
+		} else {
+			callback(null, '23.192.228.80');
+		}
+	};
+
+	describe(resolveIp, () => {
+		it('should parse inline IPs', async () => {
+			const result = await resolveIp(new URL('https://10.0.0.1'), fakeLookup);
+			expect(result.toString()).toEqual('10.0.0.1');
+		});
+
+		it('should resolve domain names', async () => {
+			const result = await resolveIp(new URL('https://localhost'), fakeLookup);
+			expect(result.toString()).toEqual('127.0.0.1');
+		});
+	});
+
+	describe(isPrivateUrl, () => {
+		it('should return false when URL is public host', async () => {
+			const result = await isPrivateUrl(new URL('https://example.com'), fakeLookup);
+			expect(result).toBe(false);
+		});
+
+		it('should return true when URL is private host', async () => {
+			const result = await isPrivateUrl(new URL('https://localhost'), fakeLookup);
+			expect(result).toBe(true);
+		});
+
+		it('should return false when IP is public', async () => {
+			const result = await isPrivateUrl(new URL('https://23.192.228.80'), fakeLookup);
+			expect(result).toBe(false);
+		});
+
+		it('should return true when IP is private', async () => {
+			const result = await isPrivateUrl(new URL('https://127.0.0.1'), fakeLookup);
+			expect(result).toBe(true);
+		});
+
+		it('should return true when IP is private with port and path', async () => {
+			const result = await isPrivateUrl(new URL('https://127.0.0.1:443/some/path'), fakeLookup);
+			expect(result).toBe(true);
+		});
+	});
+
 	describe('validateSocketConnect', () => {
 		let fakeSocket: Socket;
 		let fakeSocketMutable: {
diff --git a/packages/backend/test/unit/core/activitypub/ApUtilityService.ts b/packages/backend/test/unit/core/activitypub/ApUtilityService.ts
index 325a94dc5a..7b564b1fdd 100644
--- a/packages/backend/test/unit/core/activitypub/ApUtilityService.ts
+++ b/packages/backend/test/unit/core/activitypub/ApUtilityService.ts
@@ -3,30 +3,52 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import type { UtilityService } from '@/core/UtilityService.js';
 import type { IObject } from '@/core/activitypub/type.js';
 import type { EnvService } from '@/core/EnvService.js';
+import type { MiMeta } from '@/models/Meta.js';
+import type { Config } from '@/config.js';
+import type { LoggerService } from '@/core/LoggerService.js';
+import Logger from '@/logger.js';
 import { ApUtilityService } from '@/core/activitypub/ApUtilityService.js';
+import { UtilityService } from '@/core/UtilityService.js';
 
 describe(ApUtilityService, () => {
 	let serviceUnderTest: ApUtilityService;
 	let env: Record<string, string>;
 
 	beforeEach(() => {
-		const utilityService = {
-			punyHostPSLDomain(input: string) {
-				const host = new URL(input).host;
-				const parts = host.split('.');
-				return `${parts[parts.length - 2]}.${parts[parts.length - 1]}`;
-			},
-		} as unknown as UtilityService;
-
 		env = {};
 		const envService = {
 			env,
 		} as unknown as EnvService;
 
-		serviceUnderTest = new ApUtilityService(utilityService, envService);
+		const config = {
+			host: 'example.com',
+			blockedHosts: [],
+			silencedHosts: [],
+			mediaSilencedHosts: [],
+			federationHosts: [],
+			bubbleInstances: [],
+			deliverSuspendedSoftware: [],
+			federation: 'all',
+		} as unknown as Config;
+		const meta = {
+
+		} as MiMeta;
+
+		const utilityService = new UtilityService(config, meta, envService);
+
+		const loggerService = {
+			getLogger(domain: string) {
+				const logger = new Logger(domain);
+				Object.defineProperty(logger, 'log', {
+					value: () => {},
+				});
+				return logger;
+			},
+		} as unknown as LoggerService;
+
+		serviceUnderTest = new ApUtilityService(utilityService, loggerService);
 	});
 
 	describe('assertIdMatchesUrlAuthority', () => {
@@ -351,4 +373,102 @@ describe(ApUtilityService, () => {
 			expect(result).toBe('http://example.com/1');
 		});
 	});
+
+	describe('sanitizeInlineObject', () => {
+		it('should exclude nested arrays', () => {
+			const input = {
+				test: [[]] as unknown as string[],
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(false);
+		});
+
+		it('should exclude incorrect type', () => {
+			const input = {
+				test: 0 as unknown as string,
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(false);
+		});
+
+		it('should exclude missing ID', () => {
+			const input = {
+				test: {
+					id: undefined,
+				},
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(false);
+		});
+
+		it('should exclude wrong host', () => {
+			const input = {
+				test: 'https://wrong.com/object',
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(false);
+		});
+
+		it('should exclude invalid URLs', () => {
+			const input = {
+				test: 'https://user@example.com/object',
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(false);
+		});
+
+		it('should accept string', () => {
+			const input = {
+				test: 'https://example.com/object',
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(true);
+		});
+
+		it('should accept array of string', () => {
+			const input = {
+				test: ['https://example.com/object'],
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(true);
+		});
+
+		it('should accept object', () => {
+			const input = {
+				test: {
+					id: 'https://example.com/object',
+				},
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(true);
+		});
+
+		it('should accept array of object', () => {
+			const input = {
+				test: [{
+					id: 'https://example.com/object',
+				}],
+			};
+
+			const result = serviceUnderTest.sanitizeInlineObject(input, 'test', 'https://example.com/actor', 'example.com');
+
+			expect(result).toBe(true);
+		});
+	});
 });