diff --git a/locales/en-US.yml b/locales/en-US.yml
index ed2221fc5..ece1ec8ca 100644
--- a/locales/en-US.yml
+++ b/locales/en-US.yml
@@ -487,6 +487,7 @@ usernameInvalidFormat: "You can use upper- and lowercase letters, numbers, and u
 tooShort: "Too short"
 tooLong: "Too long"
 weakPassword: "Weak password"
+leakedPassword: "This password has been leaked {n} times in other services"
 normalPassword: "Average password"
 strongPassword: "Strong password"
 passwordMatched: "Matches"
diff --git a/locales/index.d.ts b/locales/index.d.ts
index 3233091bd..b8a8b9586 100644
--- a/locales/index.d.ts
+++ b/locales/index.d.ts
@@ -1964,6 +1964,10 @@ export interface Locale extends ILocale {
      * 弱いパスワード
      */
     "weakPassword": string;
+    /**
+     * このパスワードは他のサービスで{n}回以上流出しています
+     */
+    "leakedPassword": ParameterizedString<"n">;
     /**
      * 普通のパスワード
      */
diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index f4899dafd..2317bf88d 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -487,6 +487,7 @@ usernameInvalidFormat: "a~z、A~Z、0~9、_が使えます"
 tooShort: "短すぎます"
 tooLong: "長すぎます"
 weakPassword: "弱いパスワード"
+leakedPassword: "このパスワードは他のサービスで{n}回以上流出しています"
 normalPassword: "普通のパスワード"
 strongPassword: "強いパスワード"
 passwordMatched: "一致しました"
diff --git a/locales/ko-KR.yml b/locales/ko-KR.yml
index 8372df7d5..a58b4381e 100644
--- a/locales/ko-KR.yml
+++ b/locales/ko-KR.yml
@@ -486,6 +486,7 @@ usernameInvalidFormat: "a~z, A~Z, 0-9, _를 사용할 수 있습니다"
 tooShort: "너무 짧습니다"
 tooLong: "너무 깁니다"
 weakPassword: "약한 비밀번호"
+leakedPassword: "이 비밀번호는 다른 서비스에서 {n}회 이상 유출되었습니다"
 normalPassword: "좋은 비밀번호"
 strongPassword: "강한 비밀번호"
 passwordMatched: "일치합니다"
diff --git a/packages/frontend/src/components/MkSignupDialog.form.vue b/packages/frontend/src/components/MkSignupDialog.form.vue
index 5f08e416c..0eef175cb 100644
--- a/packages/frontend/src/components/MkSignupDialog.form.vue
+++ b/packages/frontend/src/components/MkSignupDialog.form.vue
@@ -14,7 +14,7 @@ SPDX-License-Identifier: AGPL-3.0-only
 				<template #label>{{ i18n.ts.invitationCode }}</template>
 				<template #prefix><i class="ti ti-key"></i></template>
 			</MkInput>
-			<MkInput v-model="username" type="text" pattern="^[a-zA-Z0-9_]{1,20}$" :spellcheck="false" autocomplete="username" required data-cy-signup-username @update:modelValue="onChangeUsername">
+			<MkInput v-model="username" :debounce="true" type="text" pattern="^[a-zA-Z0-9_]{1,20}$" :spellcheck="false" autocomplete="username" required data-cy-signup-username @update:modelValue="onChangeUsername">
 				<template #label>{{ i18n.ts.username }} <div v-tooltip:dialog="i18n.ts.usernameInfo" class="_button _help"><i class="ti ti-help-circle"></i></div></template>
 				<template #prefix>@</template>
 				<template #suffix>@{{ host }}</template>
@@ -45,11 +45,15 @@ SPDX-License-Identifier: AGPL-3.0-only
 					<span v-else-if="emailState === 'error'" style="color: var(--error)"><i class="ti ti-alert-triangle ti-fw"></i> {{ i18n.ts.error }}</span>
 				</template>
 			</MkInput>
-			<MkInput v-model="password" type="password" autocomplete="new-password" required data-cy-signup-password @update:modelValue="onChangePassword">
-				<template #label>{{ i18n.ts.password }}</template>
+			<MkInput v-model="password" :debounce="true" type="password" autocomplete="new-password" required data-cy-signup-password @update:modelValue="onChangePassword">
+				<template #label>
+					{{ i18n.ts.password }} <a href="https://haveibeenpwned.com/Passwords" target="_blank" rel="nofollow noopener"><span :class="$style.hibpLogo">leak checked by <span>';--hibp?</span></span></a>
+				</template>
 				<template #prefix><i class="ti ti-lock"></i></template>
 				<template #caption>
-					<span v-if="passwordStrength == 'low'" style="color: var(--error)"><i class="ti ti-alert-triangle ti-fw"></i> {{ i18n.ts.weakPassword }}</span>
+					<span v-if="passwordStrength == 'wait'" style="color:#999"><MkLoading :em="true"/> {{ i18n.ts.checking }}</span>
+					<span v-if="passwordStrength == 'low' && isLeaked" style="color: var(--error)"><i class="ti ti-alert-triangle ti-fw"></i> {{ i18n.tsx.leakedPassword({ n: leakedCount }) }}</span>
+					<span v-else-if="passwordStrength == 'low'" style="color: var(--error)"><i class="ti ti-alert-triangle ti-fw"></i> {{ i18n.ts.weakPassword }}</span>
 					<span v-if="passwordStrength == 'medium'" style="color: var(--warn)"><i class="ti ti-check ti-fw"></i> {{ i18n.ts.normalPassword }}</span>
 					<span v-if="passwordStrength == 'high'" style="color: var(--success)"><i class="ti ti-check ti-fw"></i> {{ i18n.ts.strongPassword }}</span>
 				</template>
@@ -115,7 +119,9 @@ const invitationCode = ref<string>('');
 const email = ref('');
 const usernameState = ref<null | 'wait' | 'ok' | 'unavailable' | 'error' | 'invalid-format' | 'min-range' | 'max-range'>(null);
 const emailState = ref<null | 'wait' | 'ok' | 'unavailable:used' | 'unavailable:format' | 'unavailable:disposable' | 'unavailable:banned' | 'unavailable:mx' | 'unavailable:smtp' | 'unavailable' | 'error'>(null);
-const passwordStrength = ref<'' | 'low' | 'medium' | 'high'>('');
+const passwordStrength = ref<'' | 'wait' | 'low' | 'medium' | 'high'>('');
+const isLeaked = ref(false);
+const leakedCount = ref(0);
 const passwordRetypeState = ref<null | 'match' | 'not-match'>(null);
 const submitting = ref<boolean>(false);
 const hCaptchaResponse = ref<string | null>(null);
@@ -124,6 +130,7 @@ const reCaptchaResponse = ref<string | null>(null);
 const turnstileResponse = ref<string | null>(null);
 const usernameAbortController = ref<null | AbortController>(null);
 const emailAbortController = ref<null | AbortController>(null);
+const passwordAbortController = ref<null | AbortController>(null);
 
 const shouldDisableSubmitting = computed((): boolean => {
 	return submitting.value ||
@@ -132,11 +139,12 @@ const shouldDisableSubmitting = computed((): boolean => {
 		instance.enableRecaptcha && !reCaptchaResponse.value ||
 		instance.enableTurnstile && !turnstileResponse.value ||
 		instance.emailRequiredForSignup && emailState.value !== 'ok' ||
+		(passwordStrength.value !== 'medium' && passwordStrength.value !== 'high') ||
 		usernameState.value !== 'ok' ||
 		passwordRetypeState.value !== 'match';
 });
 
-function getPasswordStrength(source: string): number {
+async function getPasswordStrength(source: string): Promise<number> {
 	let strength = 0;
 	let power = 0.018;
 
@@ -157,6 +165,46 @@ function getPasswordStrength(source: string): number {
 
 	strength = power * source.length;
 
+	// check HIBP 3 chars or more
+	if (passwordAbortController.value != null) {
+		passwordAbortController.value.abort();
+	}
+
+	if (source.length >= 3) {
+		passwordStrength.value = 'wait';
+		passwordAbortController.value = new AbortController();
+
+		const hash = await crypto.subtle.digest('SHA-1', new TextEncoder().encode(source));
+		const hashHex = Array.from(new Uint8Array(hash)).map(b => b.toString(16).padStart(2, '0')).join('');
+		const hashPrefix = hashHex.slice(0, 5).toUpperCase();
+		const hashSuffix = hashHex.slice(5).toUpperCase();
+		await fetch(`https://api.pwnedpasswords.com/range/${hashPrefix}`, { signal: passwordAbortController.value.signal })
+			.then(response => {
+				if (!response.ok) {
+					throw new Error(`HTTP error! status: ${response.status}`);
+				}
+				return response.text();
+			})
+			.then(text => {
+				const lines = text.split('\n');
+				const line = lines.find(l => l.startsWith(hashSuffix));
+				if (line) {
+					leakedCount.value = parseInt(line.split(':')[1]);
+					isLeaked.value = true;
+					strength = 0;
+				} else {
+					isLeaked.value = false;
+				}
+			})
+			.catch(() => {
+				leakedCount.value = 0;
+				isLeaked.value = false;
+			});
+	} else {
+		leakedCount.value = 0;
+		isLeaked.value = false;
+	}
+
 	return Math.max(0, Math.min(1, strength));
 }
 
@@ -226,14 +274,16 @@ function onChangeEmail(): void {
 	});
 }
 
-function onChangePassword(): void {
+async function onChangePassword(): Promise<void> {
 	if (password.value === '') {
 		passwordStrength.value = '';
 		return;
 	}
 
-	const strength = getPasswordStrength(password.value);
+	const strength = await getPasswordStrength(password.value);
 	passwordStrength.value = strength > 0.7 ? 'high' : strength > 0.3 ? 'medium' : 'low';
+
+	if (passwordRetypeState.value === 'match') onChangePasswordRetype();
 }
 
 function onChangePasswordRetype(): void {
@@ -304,4 +354,26 @@ async function onSubmit(): Promise<void> {
 .captcha {
 	margin: 16px 0;
 }
+
+.hibpLogo {
+	background: linear-gradient(45deg, #616c70, #626262);
+	color: #fefefe;
+	display: inline-flex;
+	padding-left: 8px;
+	margin-left: 4px;
+	font-size: 0.8em;
+	border-radius: 6px;
+	overflow: hidden;
+	align-items: center;
+	transform: translateY(-1px);
+
+	span {
+		background: linear-gradient(45deg, #255e81, #338cac);
+		font-size: 1.4em;
+		padding: 2px 8px;
+		height: auto;
+		margin-left: 8px;
+		font-weight: bold;
+	}
+}
 </style>
diff --git a/packages/frontend/src/index.html b/packages/frontend/src/index.html
index 08ff0c58d..bbec8e06e 100644
--- a/packages/frontend/src/index.html
+++ b/packages/frontend/src/index.html
@@ -22,7 +22,7 @@
 			style-src 'self' 'unsafe-inline';
 			img-src 'self' data: blob: www.google.com xn--931a.moe localhost:3000 localhost:5173 127.0.0.1:5173 127.0.0.1:3000;
 			media-src 'self' localhost:3000 localhost:5173 127.0.0.1:5173 127.0.0.1:3000;
-			connect-src 'self' localhost:3000 localhost:5173 127.0.0.1:5173 127.0.0.1:3000 https://newassets.hcaptcha.com;
+			connect-src 'self' localhost:3000 localhost:5173 127.0.0.1:5173 127.0.0.1:3000 https://newassets.hcaptcha.com https://api.pwnedpasswords.com;
 			frame-src *;"
 	/>
 	<meta property="og:site_name" content="[DEV BUILD] Misskey" />