diff --git a/core/admin/assets/content/assets/app.js b/core/admin/assets/content/assets/app.js
index 03ea6215..b0d48470 100644
--- a/core/admin/assets/content/assets/app.js
+++ b/core/admin/assets/content/assets/app.js
@@ -3,6 +3,56 @@ require('./app.css');
 import logo from './mailu.png';
 import modules from "./*.json";
 
+// Inspired from https://github.com/mehdibo/hibp-js/blob/master/hibp.js
+function sha1(string){
+    var buffer = new TextEncoder("utf-8").encode(string);
+    return crypto.subtle.digest("SHA-1", buffer).then(function (buffer) {
+        // Get the hex code
+        var hexCodes = [];
+        var view = new DataView(buffer);
+        for (var i = 0; i < view.byteLength; i += 4) {
+            // Using getUint32 reduces the number of iterations needed (we process 4 bytes each time)
+            var value = view.getUint32(i)
+            // toString(16) will give the hex representation of the number without padding
+            var stringValue = value.toString(16)
+            // We use concatenation and slice for padding
+            var padding = '00000000'
+            var paddedValue = (padding + stringValue).slice(-padding.length)
+            hexCodes.push(paddedValue);
+        }
+        // Join all the hex strings into one
+        return hexCodes.join("");
+    });
+}
+
+function hibpCheck(pwd){
+    // We hash the pwd first
+    sha1(pwd).then(function(hash){
+        // We send the first 5 chars of the hash to hibp's API
+        const req = new XMLHttpRequest();
+        req.addEventListener("load", function(){
+            // When we get back a response from the server
+            // We create an array of lines and loop through them
+            const resp = this.responseText.split('\n');
+            const hashSub = hash.slice(5).toUpperCase();
+            for(index in resp){
+                // Check if the line matches the rest of the hash
+                if(resp[index].substring(0, 35) == hashSub){
+                    var val = resp[index].split(":")[1]
+                    if (val > 0) {
+                        $("#pwned").value = val;
+		    }
+                    return; // If found no need to continue the loop
+                }
+            }
+	    $("#pwned").value = 0;
+        });
+        req.open('GET', 'https://api.pwnedpasswords.com/range/'+hash.substr(0, 5));
+	req.setRequestHeader('Add-Padding', 'true');
+        req.send();
+    });
+}
+
 // TODO: conditionally (or lazy) load select2 and dataTable
 $('document').ready(function() {
 
@@ -75,5 +125,12 @@ $('document').ready(function() {
         $('form :input').prop('disabled', true);
     }
 
+    if (window.isSecureContext) {
+        $("#HIBPpw").change(function(){
+            hibpCheck($("#HIBPpw").value);
+            return true;
+        })
+    }
+
 });
 
diff --git a/core/admin/mailu/sso/forms.py b/core/admin/mailu/sso/forms.py
index 5cf38dbe..530fc1c2 100644
--- a/core/admin/mailu/sso/forms.py
+++ b/core/admin/mailu/sso/forms.py
@@ -7,5 +7,6 @@ class LoginForm(flask_wtf.FlaskForm):
         csrf = False
     email = fields.StringField(_('E-mail'), [validators.Email(), validators.DataRequired()])
     pw = fields.PasswordField(_('Password'), [validators.DataRequired()])
+    pwned = fields.HiddenField(label='',default=-1)
     submitWebmail = fields.SubmitField(_('Sign in'))
     submitAdmin = fields.SubmitField(_('Sign in'))
diff --git a/core/admin/mailu/sso/views/base.py b/core/admin/mailu/sso/views/base.py
index 00b6912d..34ba98b5 100644
--- a/core/admin/mailu/sso/views/base.py
+++ b/core/admin/mailu/sso/views/base.py
@@ -40,7 +40,10 @@ def login():
             flask_login.login_user(user)
             response = flask.redirect(destination)
             response.set_cookie('rate_limit', utils.limiter.device_cookie(username), max_age=31536000, path=flask.url_for('sso.login'), secure=app.config['SESSION_COOKIE_SECURE'], httponly=True)
-            flask.current_app.logger.info(f'Login succeeded for {username} from {client_ip}.')
+            flask.current_app.logger.info(f'Login succeeded for {username} from {client_ip} pwned={form.pwned.data}.')
+            breaches = int(form.pwned.data)
+            if breaches > 0:
+                flask.flash(f"Your password appears in {breaches} data breaches! Please change it.", "error")
             return response
         else:
             utils.limiter.rate_limit_user(username, client_ip, device_cookie, device_cookie_username) if models.User.get(username) else utils.limiter.rate_limit_ip(client_ip)
diff --git a/core/admin/mailu/ui/forms.py b/core/admin/mailu/ui/forms.py
index 683db7ae..67e4b674 100644
--- a/core/admin/mailu/ui/forms.py
+++ b/core/admin/mailu/ui/forms.py
@@ -59,6 +59,7 @@ class DomainSignupForm(flask_wtf.FlaskForm):
     localpart = fields.StringField(_('Initial admin'), [validators.DataRequired()])
     pw = fields.PasswordField(_('Admin password'), [validators.DataRequired()])
     pw2 = fields.PasswordField(_('Confirm password'), [validators.EqualTo('pw')])
+    pwned = fields.HiddenField(label='',default=-1)
     captcha = flask_wtf.RecaptchaField()
     submit = fields.SubmitField(_('Create'))
 
@@ -79,6 +80,7 @@ class UserForm(flask_wtf.FlaskForm):
     localpart = fields.StringField(_('E-mail'), [validators.DataRequired(), validators.Regexp(LOCALPART_REGEX)])
     pw = fields.PasswordField(_('Password'))
     pw2 = fields.PasswordField(_('Confirm password'), [validators.EqualTo('pw')])
+    pwned = fields.HiddenField(label='',default=-1)
     quota_bytes = fields_.IntegerSliderField(_('Quota'), default=10**9)
     enable_imap = fields.BooleanField(_('Allow IMAP access'), default=True)
     enable_pop = fields.BooleanField(_('Allow POP3 access'), default=True)
@@ -92,6 +94,7 @@ class UserSignupForm(flask_wtf.FlaskForm):
     localpart = fields.StringField(_('Email address'), [validators.DataRequired(), validators.Regexp(LOCALPART_REGEX)])
     pw = fields.PasswordField(_('Password'), [validators.DataRequired()])
     pw2 = fields.PasswordField(_('Confirm password'), [validators.EqualTo('pw')])
+    pwned = fields.HiddenField(label='',default=-1)
     submit = fields.SubmitField(_('Sign up'))
 
 class UserSignupFormCaptcha(UserSignupForm):
@@ -111,6 +114,7 @@ class UserSettingsForm(flask_wtf.FlaskForm):
 class UserPasswordForm(flask_wtf.FlaskForm):
     pw = fields.PasswordField(_('Password'), [validators.DataRequired()])
     pw2 = fields.PasswordField(_('Password check'), [validators.DataRequired()])
+    pwned = fields.HiddenField(label='',default=-1)
     submit = fields.SubmitField(_('Update password'))
 
 
diff --git a/core/admin/mailu/ui/views/domains.py b/core/admin/mailu/ui/views/domains.py
index 4010e2ae..4b237ca0 100644
--- a/core/admin/mailu/ui/views/domains.py
+++ b/core/admin/mailu/ui/views/domains.py
@@ -93,6 +93,10 @@ def domain_signup(domain_name=None):
         del form.pw
         del form.pw2
     if form.validate_on_submit():
+        breaches = int(form.pwned.data)
+        if breaches > 0:
+            flask.flash(f"This password appears in {breaches} data breaches! Please change it.", "error")
+            return flask.render_template('domain/signup.html', form=form)
         conflicting_domain = models.Domain.query.get(form.name.data)
         conflicting_alternative = models.Alternative.query.get(form.name.data)
         conflicting_relay = models.Relay.query.get(form.name.data)
diff --git a/core/admin/mailu/ui/views/users.py b/core/admin/mailu/ui/views/users.py
index c4b26036..2bd664b5 100644
--- a/core/admin/mailu/ui/views/users.py
+++ b/core/admin/mailu/ui/views/users.py
@@ -28,6 +28,11 @@ def user_create(domain_name):
         form.quota_bytes.validators = [
             wtforms.validators.NumberRange(max=domain.max_quota_bytes)]
     if form.validate_on_submit():
+        breaches = int(form.pwned.data)
+        if breaches > 0:
+            flask.flash(f"This password appears in {breaches} data breaches! Please change it.", "error")
+            return flask.render_template('user/create.html',
+                domain=domain, form=form)
         if domain.has_email(form.localpart.data):
             flask.flash('Email is already used', 'error')
         else:
@@ -60,6 +65,11 @@ def user_edit(user_email):
         form.quota_bytes.validators = [
             wtforms.validators.NumberRange(max=max_quota_bytes)]
     if form.validate_on_submit():
+        breaches = int(form.pwned.data)
+        if breaches > 0:
+            flask.flash(f"This password appears in {breaches} data breaches! Please change it.", "error")
+            return flask.render_template('user/edit.html', form=form, user=user,
+                domain=user.domain, max_quota_bytes=max_quota_bytes)
         form.populate_obj(user)
         if form.pw.data:
             user.set_password(form.pw.data)
@@ -119,6 +129,10 @@ def user_password(user_email):
         if form.pw.data != form.pw2.data:
             flask.flash('Passwords do not match', 'error')
         else:
+            breaches = int(form.pwned.data)
+            if breaches > 0:
+                flask.flash(f"This password appears in {breaches} data breaches! Please change it.", "error")
+                return flask.render_template('user/password.html', form=form, user=user)
             flask.session.regenerate()
             user.set_password(form.pw.data)
             models.db.session.commit()
@@ -170,6 +184,10 @@ def user_signup(domain_name=None):
         if domain.has_email(form.localpart.data) or models.Alias.resolve(form.localpart.data, domain_name):
             flask.flash('Email is already used', 'error')
         else:
+            breaches = int(form.pwned.data)
+            if breaches > 0:
+                flask.flash(f"This password appears in {breaches} data breaches! Please change it.", "error")
+                return flask.render_template('user/signup.html', domain=domain, form=form)
             flask.session.regenerate()
             user = models.User(domain=domain)
             form.populate_obj(user)