enhance: replace signin CAPTCHA with rate limit (#8740)

* enhance: rate limit works without signed in user

* fix: make limit key required for limiter

As before the fallback limiter key will be set from the endpoint name.

* enhance: use limiter for signin

* Revert "CAPTCHA求めるのは2fa認証が無効になっているときだけにした"

This reverts commit 02a43a310f6ad0cc9e9beccc26e51ab5b339e15f.

* Revert "feat: make captcha required when signin to improve security"

This reverts commit b21b0580058c14532ff3f4033e2a9147643bfca6.

* fix undefined reference

* fix: better error message

* enhance: only handle prefix of IPv6

4 files changed, 64 insertions, 53 deletions

diff --git a/packages/backend/src/server/api/call.ts b/packages/backend/src/server/api/call.ts
index 9a85e4565b..fbe25e1732 100644
--- a/packages/backend/src/server/api/call.ts
+++ b/packages/backend/src/server/api/call.ts
@@ -2,10 +2,11 @@ import Koa from 'koa';
 import { performance } from 'perf_hooks';
 import { limiter } from './limiter.js';
 import { CacheableLocalUser, User } from '@/models/entities/user.js';
-import endpoints, { IEndpoint } from './endpoints.js';
+import endpoints, { IEndpointMeta } from './endpoints.js';
 import { ApiError } from './error.js';
 import { apiLogger } from './logger.js';
 import { AccessToken } from '@/models/entities/access-token.js';
+import IPCIDR from 'ip-cidr';
 
 const accessDenied = {
 	message: 'Access denied.',
@@ -15,6 +16,7 @@ const accessDenied = {
 
 export default async (endpoint: string, user: CacheableLocalUser | null | undefined, token: AccessToken | null | undefined, data: any, ctx?: Koa.Context) => {
 	const isSecure = user != null && token == null;
+	const isModerator = user != null && (user.isModerator || user.isAdmin);
 
 	const ep = endpoints.find(e => e.name === endpoint);
 
@@ -31,6 +33,37 @@ export default async (endpoint: string, user: CacheableLocalUser | null | undefi
 		throw new ApiError(accessDenied);
 	}
 
+	if (ep.meta.requireCredential && ep.meta.limit && !isModerator) {
+		// koa will automatically load the `X-Forwarded-For` header if `proxy: true` is configured in the app.
+		let limitActor: string;
+		if (user) {
+			limitActor = user.id;
+		} else {
+			// because a single person may control many IPv6 addresses,
+			// only a /64 subnet prefix of any IP will be taken into account.
+			// (this means for IPv4 the entire address is used)
+			const ip = IPCIDR.createAddress(ctx.ip).mask(64);
+
+			limitActor = 'ip-' + parseInt(ip, 2).toString(36);
+		}
+
+		const limit = Object.assign({}, ep.meta.limit);
+
+		if (!limit.key) {
+			limit.key = ep.name;
+		}
+
+		// Rate limit
+		await limiter(limit as IEndpointMeta['limit'] & { key: NonNullable<string> }, limitActor).catch(e => {
+			throw new ApiError({
+				message: 'Rate limit exceeded. Please try again later.',
+				code: 'RATE_LIMIT_EXCEEDED',
+				id: 'd5826d14-3982-4d2e-8011-b9e9f02499ef',
+				httpStatusCode: 429,
+			});
+		});
+	}
+
 	if (ep.meta.requireCredential && user == null) {
 		throw new ApiError({
 			message: 'Credential required.',
@@ -53,7 +86,7 @@ export default async (endpoint: string, user: CacheableLocalUser | null | undefi
 		throw new ApiError(accessDenied, { reason: 'You are not the admin.' });
 	}
 
-	if (ep.meta.requireModerator && !user!.isAdmin && !user!.isModerator) {
+	if (ep.meta.requireModerator && !isModerator) {
 		throw new ApiError(accessDenied, { reason: 'You are not a moderator.' });
 	}
 
@@ -65,18 +98,6 @@ export default async (endpoint: string, user: CacheableLocalUser | null | undefi
 		});
 	}
 
-	if (ep.meta.requireCredential && ep.meta.limit && !user!.isAdmin && !user!.isModerator) {
-		// Rate limit
-		await limiter(ep as IEndpoint & { meta: { limit: NonNullable<IEndpoint['meta']['limit']> } }, user!).catch(e => {
-			throw new ApiError({
-				message: 'Rate limit exceeded. Please try again later.',
-				code: 'RATE_LIMIT_EXCEEDED',
-				id: 'd5826d14-3982-4d2e-8011-b9e9f02499ef',
-				httpStatusCode: 429,
-			});
-		});
-	}
-
 	// Cast non JSON input
 	if (ep.meta.requireFile && ep.params.properties) {
 		for (const k of Object.keys(ep.params.properties)) {
diff --git a/packages/backend/src/server/api/endpoints.ts b/packages/backend/src/server/api/endpoints.ts
index e2db03f13a..1e7afd8cdd 100644
--- a/packages/backend/src/server/api/endpoints.ts
+++ b/packages/backend/src/server/api/endpoints.ts
@@ -654,7 +654,6 @@ export interface IEndpointMeta {
 	/**
 	 * エンドポイントのリミテーションに関するやつ
 	 * 省略した場合はリミテーションは無いものとして解釈されます。
-	 * また、withCredential が false の場合はリミテーションを行うことはできません。
 	 */
 	readonly limit?: {
 
diff --git a/packages/backend/src/server/api/limiter.ts b/packages/backend/src/server/api/limiter.ts
index e74db8466e..23430cf8b6 100644
--- a/packages/backend/src/server/api/limiter.ts
+++ b/packages/backend/src/server/api/limiter.ts
@@ -1,25 +1,17 @@
 import Limiter from 'ratelimiter';
 import { redisClient } from '../../db/redis.js';
-import { IEndpoint } from './endpoints.js';
-import * as Acct from '@/misc/acct.js';
+import { IEndpointMeta } from './endpoints.js';
 import { CacheableLocalUser, User } from '@/models/entities/user.js';
 import Logger from '@/services/logger.js';
 
 const logger = new Logger('limiter');
 
-export const limiter = (endpoint: IEndpoint & { meta: { limit: NonNullable<IEndpoint['meta']['limit']> } }, user: CacheableLocalUser) => new Promise<void>((ok, reject) => {
-	const limitation = endpoint.meta.limit;
-
-	const key = Object.prototype.hasOwnProperty.call(limitation, 'key')
-		? limitation.key
-		: endpoint.name;
-
-	const hasShortTermLimit =
-		Object.prototype.hasOwnProperty.call(limitation, 'minInterval');
+export const limiter = (limitation: IEndpointMeta['limit'] & { key: NonNullable<string> }, actor: string) => new Promise<void>((ok, reject) => {
+	const hasShortTermLimit = typeof limitation.minInterval === 'number';
 
 	const hasLongTermLimit =
-		Object.prototype.hasOwnProperty.call(limitation, 'duration') &&
-		Object.prototype.hasOwnProperty.call(limitation, 'max');
+		typeof limitation.duration === 'number' &&
+		typeof limitation.max === 'number';
 
 	if (hasShortTermLimit) {
 		min();
@@ -32,7 +24,7 @@ export const limiter = (endpoint: IEndpoint & { meta: { limit: NonNullable<IEndp
 	// Short-term limit
 	function min(): void {
 		const minIntervalLimiter = new Limiter({
-			id: `${user.id}:${key}:min`,
+			id: `${actor}:${limitation.key}:min`,
 			duration: limitation.minInterval,
 			max: 1,
 			db: redisClient,
@@ -43,7 +35,7 @@ export const limiter = (endpoint: IEndpoint & { meta: { limit: NonNullable<IEndp
 				return reject('ERR');
 			}
 
-			logger.debug(`@${Acct.toString(user)} ${endpoint.name} min remaining: ${info.remaining}`);
+			logger.debug(`${actor} ${limitation.key} min remaining: ${info.remaining}`);
 
 			if (info.remaining === 0) {
 				reject('BRIEF_REQUEST_INTERVAL');
@@ -60,7 +52,7 @@ export const limiter = (endpoint: IEndpoint & { meta: { limit: NonNullable<IEndp
 	// Long term limit
 	function max(): void {
 		const limiter = new Limiter({
-			id: `${user.id}:${key}`,
+			id: `${actor}:${limitation.key}`,
 			duration: limitation.duration,
 			max: limitation.max,
 			db: redisClient,
@@ -71,7 +63,7 @@ export const limiter = (endpoint: IEndpoint & { meta: { limit: NonNullable<IEndp
 				return reject('ERR');
 			}
 
-			logger.debug(`@${Acct.toString(user)} ${endpoint.name} max remaining: ${info.remaining}`);
+			logger.debug(`${actor} ${limitation.key} max remaining: ${info.remaining}`);
 
 			if (info.remaining === 0) {
 				reject('RATE_LIMIT_EXCEEDED');
diff --git a/packages/backend/src/server/api/private/signin.ts b/packages/backend/src/server/api/private/signin.ts
index 0024b8ce3e..b304550e29 100644
--- a/packages/backend/src/server/api/private/signin.ts
+++ b/packages/backend/src/server/api/private/signin.ts
@@ -1,25 +1,21 @@
-import { randomBytes } from 'node:crypto';
 import Koa from 'koa';
 import bcrypt from 'bcryptjs';
 import * as speakeasy from 'speakeasy';
-import { IsNull } from 'typeorm';
+import signin from '../common/signin.js';
 import config from '@/config/index.js';
 import { Users, Signins, UserProfiles, UserSecurityKeys, AttestationChallenges } from '@/models/index.js';
 import { ILocalUser } from '@/models/entities/user.js';
 import { genId } from '@/misc/gen-id.js';
-import { fetchMeta } from '@/misc/fetch-meta.js';
-import { verifyHcaptcha, verifyRecaptcha } from '@/misc/captcha.js';
 import { verifyLogin, hash } from '../2fa.js';
-import signin from '../common/signin.js';
+import { randomBytes } from 'node:crypto';
+import { IsNull } from 'typeorm';
+import { limiter } from '../limiter.js';
 
 export default async (ctx: Koa.Context) => {
 	ctx.set('Access-Control-Allow-Origin', config.url);
 	ctx.set('Access-Control-Allow-Credentials', 'true');
 
 	const body = ctx.request.body as any;
-
-	const instance = await fetchMeta(true);
-
 	const username = body['username'];
 	const password = body['password'];
 	const token = body['token'];
@@ -29,6 +25,21 @@ export default async (ctx: Koa.Context) => {
 		ctx.body = { error };
 	}
 
+	try {
+		// not more than 1 attempt per second and not more than 10 attempts per hour
+		await limiter({ key: 'signin', duration: 60 * 60 * 1000, max: 10, minInterval: 1000 }, ctx.ip);
+	} catch (err) {
+		ctx.status = 429;
+		ctx.body = {
+			error: {
+				message: 'Too many failed attempts to sign in. Try again later.',
+				code: 'TOO_MANY_AUTHENTICATION_FAILURES',
+				id: '22d05606-fbcf-421a-a2db-b32610dcfd1b',
+			},
+		};
+		return;
+	}
+
 	if (typeof username !== 'string') {
 		ctx.status = 400;
 		return;
@@ -84,18 +95,6 @@ export default async (ctx: Koa.Context) => {
 	}
 
 	if (!profile.twoFactorEnabled) {
-		if (instance.enableHcaptcha && instance.hcaptchaSecretKey) {
-			await verifyHcaptcha(instance.hcaptchaSecretKey, body['hcaptcha-response']).catch(e => {
-				ctx.throw(400, e);
-			});
-		}
-	
-		if (instance.enableRecaptcha && instance.recaptchaSecretKey) {
-			await verifyRecaptcha(instance.recaptchaSecretKey, body['g-recaptcha-response']).catch(e => {
-				ctx.throw(400, e);
-			});
-		}
-	
 		if (same) {
 			signin(ctx, user);
 			return;
@@ -172,7 +171,7 @@ export default async (ctx: Koa.Context) => {
 				body.credentialId
 					.replace(/-/g, '+')
 					.replace(/_/g, '/'),
-				'base64',
+					'base64'
 			).toString('hex'),
 		});