diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 89515862..326b851d 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -9,6 +9,7 @@ This document describes changes between each past release.
 Breaking changes
 ----------------
 
+- Enable session cookie security by default (#845)
 - Drop support for Python 2 (#483)
 - Drop support for Python 3.5 (#571)
 - Drop support for MySQL (#743)
@@ -25,6 +26,7 @@ Security
 
 - Add CSRF validation on destructive actions (#796)
 - Ask for private code to delete project or project history (#796)
+- Add headers to mitigate Clickjacking, XSS, and other attacks: `X-Frame-Options`, `X-XSS-Protection`, `X-Content-Type-Options`, `Content-Security-Policy`, `Referrer-Policy` (#845)
 
 Added
 -----
diff --git a/conf/entrypoint.sh b/conf/entrypoint.sh
index dfe5e12c..e66ad7c8 100755
--- a/conf/entrypoint.sh
+++ b/conf/entrypoint.sh
@@ -21,6 +21,7 @@ ADMIN_PASSWORD = '$ADMIN_PASSWORD'
 ALLOW_PUBLIC_PROJECT_CREATION = $ALLOW_PUBLIC_PROJECT_CREATION
 ACTIVATE_ADMIN_DASHBOARD = $ACTIVATE_ADMIN_DASHBOARD
 BABEL_DEFAULT_TIMEZONE = "$BABEL_DEFAULT_TIMEZONE"
+SESSION_COOKIE_SECURE = $SESSION_COOKIE_SECURE
 EOF
 
 # Start gunicorn without forking
diff --git a/docs/configuration.rst b/docs/configuration.rst
index 29ab34f7..d29ef9f1 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -64,6 +64,21 @@ of the secret key could easily access any project and bypass the private code ve
 - **Production value:** `ihatemoney conf-example ihatemoney.cfg` sets it to
   something random, which is good.
 
+`SESSION_COOKIE_SECURE`
+-----------------------
+
+A boolean that controls whether the session cookie will be marked "secure".
+If this is the case, browsers will refuse to send the session cookie over plain HTTP.
+
+- **Default value:** ``True``
+- **Production value:** ``True`` if you run your service over HTTPS, ``False`` if you run
+  your service over plain HTTP.
+
+Note: this setting is actually interpreted by Flask, see the
+`Flask documentation`_ for details.
+
+.. _Flask documentation: https://flask.palletsprojects.com/en/2.0.x/config/#SESSION_COOKIE_SECURE
+
 `MAIL_DEFAULT_SENDER`
 ---------------------
 
diff --git a/docs/contributing.rst b/docs/contributing.rst
index 80174b76..5d597b25 100644
--- a/docs/contributing.rst
+++ b/docs/contributing.rst
@@ -104,12 +104,20 @@ You can create a ``settings.cfg`` file, with the following content::
     DEBUG = True
     SQLACHEMY_ECHO = DEBUG
 
-You can also set the `TESTING` flag to `True` so no mails are sent
-(and no exception is raised) while you're on development mode.
 Then before running the application, declare its path with ::
 
   export IHATEMONEY_SETTINGS_FILE_PATH="$(pwd)/settings.cfg"
 
+You can also set the ``TESTING`` flag to ``True`` so no mails are sent
+(and no exception is raised) while you're on development mode.
+
+In some cases, you may need to disable secure cookies by setting
+``SESSION_COOKIE_SECURE`` to ``False``. This is needed if you
+access your dev server over the network: with the default value
+of ``SESSION_COOKIE_SECURE``, the browser will refuse to send
+the session cookie over insecure HTTP, so many features of Ihatemoney
+won't work (project login, language change, etc).
+
 .. _contributing-developer:
 
 Contributing as a developer
diff --git a/docs/upgrade.rst b/docs/upgrade.rst
index ec846324..53185413 100644
--- a/docs/upgrade.rst
+++ b/docs/upgrade.rst
@@ -65,6 +65,17 @@ If so, pick the ``pip`` commands to use in the relevant section(s) of
 
 Then follow :ref:`general-procedure` from step 1. in order to complete the update.
 
+Disable session cookie security if running over plain HTTP
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+.. note:: If you are running Ihatemoney over HTTPS, no special action is required.
+
+Session cookies are now marked "secure" by default to increase security.
+
+If you run Ihatemoney over plain HTTP, you need to explicitly disable this security
+feature by setting ``SESSION_COOKIE_SECURE`` to ``False``, see :ref:`configuration`.
+
+
 Switch to MariaDB >= 10.3.2 instead of MySQL
 ++++++++++++++++++++++++++++++++++++++++++++
 
diff --git a/ihatemoney/conf-templates/ihatemoney.cfg.j2 b/ihatemoney/conf-templates/ihatemoney.cfg.j2
index 0188c6b1..13a8e9f5 100644
--- a/ihatemoney/conf-templates/ihatemoney.cfg.j2
+++ b/ihatemoney/conf-templates/ihatemoney.cfg.j2
@@ -38,3 +38,7 @@ ACTIVATE_ADMIN_DASHBOARD = False
 # You can change the timezone used to display time.  By default it will be
 #derived from the server OS.
 #BABEL_DEFAULT_TIMEZONE = "Europe/Paris"
+
+# Enable secure cookies. Requires HTTPS. Disable if you run your ihatemoney
+# service over plain HTTP.
+SESSION_COOKIE_SECURE = True
diff --git a/ihatemoney/default_settings.py b/ihatemoney/default_settings.py
index 9050bbeb..96795a01 100644
--- a/ihatemoney/default_settings.py
+++ b/ihatemoney/default_settings.py
@@ -8,6 +8,7 @@ ACTIVATE_DEMO_PROJECT = True
 ADMIN_PASSWORD = ""
 ALLOW_PUBLIC_PROJECT_CREATION = True
 ACTIVATE_ADMIN_DASHBOARD = False
+SESSION_COOKIE_SECURE = True
 SUPPORTED_LANGUAGES = [
     "de",
     "el",
diff --git a/ihatemoney/run.py b/ihatemoney/run.py
index c8fc5b25..cea6f93e 100644
--- a/ihatemoney/run.py
+++ b/ihatemoney/run.py
@@ -7,6 +7,7 @@ from flask import Flask, g, render_template, request, session
 from flask_babel import Babel, format_currency
 from flask_mail import Mail
 from flask_migrate import Migrate, stamp, upgrade
+from flask_talisman import Talisman
 from jinja2 import pass_context
 from markupsafe import Markup
 import pytz
@@ -126,6 +127,24 @@ def create_app(
         instance_relative_config=instance_relative_config,
     )
 
+    # If we need to load external JS/CSS/image resources, it needs to be added here, see
+    # https://github.com/wntrblm/flask-talisman#content-security-policy
+    csp = {
+        "default-src": ["'self'"],
+        # We have several inline javascript scripts :(
+        "script-src": ["'self'", "'unsafe-inline'"],
+        "object-src": "'none'",
+    }
+
+    Talisman(
+        app,
+        # Forcing HTTPS is the job of a reverse proxy
+        force_https=False,
+        # This is handled separately through the SESSION_COOKIE_SECURE Flask setting
+        session_cookie_secure=False,
+        content_security_policy=csp,
+    )
+
     # If a configuration object is passed, use it. Otherwise try to find one.
     load_configuration(app, configuration)
     app.wsgi_app = PrefixedWSGI(app)
diff --git a/setup.cfg b/setup.cfg
index 3bbf6f27..f58c1619 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -33,6 +33,7 @@ install_requires =
     Flask-Migrate>=2.5.3,<4  # Not following semantic versioning (e.g. https://github.com/miguelgrinberg/flask-migrate/commit/1af28ba273de6c88544623b8dc02dd539340294b)
     Flask-RESTful>=0.3.9,<1
     Flask-SQLAlchemy>=2.4,<3
+    Flask-Talisman>=0.8,<1
     Flask-WTF>=0.14.3,<1
     WTForms>=2.3.1,<2.4
     Flask>=2,<3