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+---
+title: "Slightly Improving Mailcow Security"
+date: 2022-07-18
+tags: ['Applications', 'Linux', 'Security']
+author: Tommy
+---
+
+![Mailcow](/images/mailcow.png)
+
+Mailcow is a fairly popular self-hosted mail server. If you use it, there are a few ways you can improve its security by following these steps.
+
+## Postfix Configuration
+
+Consider disabling weak ciphers and TLS versions below 1.2 in `data/conf/postfix/extra.cf`:
+
+```
+tls_high_cipherlist = ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256
+tls_preempt_cipherlist = yes
+
+smtp_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
+smtp_tls_ciphers = high
+smtp_tls_mandatory_ciphers = high
+
+smtpd_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
+smtpd_tls_ciphers = high
+smtpd_tls_mandatory_ciphers = high
+```
+
+## NGINX Configuration
+
+These security configurations can be added/modified in `data/conf/nginx/includes/site-defaults.conf`.
+
+## SSL Ciphers
+
+Consider only supporting ciphers matching that of TLSv1.3:
+
+```
+ssl_ciphers "ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256";
+```
+
+## HSTS
+
+Consider adding `includeSubDomains;`to the HSTS configuration if all of your services are using HTTPS:
+
+```
+add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload";
+```
+
+### X-XSS-Protection
+
+We will setup Content Security, so this header is no longer needed. In fact, it may do [more harm than good](https://github.com/helmetjs/helmet/issues/230). Change the setting to `0`:
+
+```
+add_header X-XSS-Protection "0";
+```
+
+### Permission Policy
+
+Mailcow does not need any special permissions to operate, except for USB which is needed to access your FIDO2 keys if you use them.
+
+Add this header to deny other permissions:
+
+```
+add_header Permissions-Policy "accelerometer=(), ambient-light-sensor=(), autoplay=(), battery=(), camera=(), clipboard-read=(), display-capture=(), document-domain=(), encrypted-media=(), fullscreen=(), geolocation=(), gyroscope=(), hid=(), idle-detection=(), interest-cohort=(), magnetometer=(), microphone=(), midi=(), payment=(), picture-in-picture=(), screen-wake-lock=(), serial=(), usb=(), sync-xhr=(), xr-spatial-tracking=()";
+```
+
+### Content Security Policy
+
+Use the following as your [Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP#:~:text=Content%20Security%20Policy%20(CSP)%20is,site%20defacement%2C%20to%20malware%20distribution.):
+
+#### If you use Gravatar with SOGo
+
+```
+add_header Content-Security-Policy "default-src 'none'; connect-src 'self' https://api.github.com; font-src 'self' https://fonts.gstatic.com; img-src 'self' data:; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; frame-ancestors 'none'; block-all-mixed-content; base-uri 'none'";
+```
+
+#### If you do not use Gravatar with SOGo
+
+```
+add_header Content-Security-Policy "default-src 'none'; connect-src 'self' https://api.github.com https://www.gravatar.com; font-src 'self' https://fonts.gstatic.com; img-src 'self' data: https://www.gravatar.com; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; frame-ancestors 'none'; block-all-mixed-content; base-uri 'none'";
+```
+
+### Cross-Origin Opener, Resource, and Embedder Policies
+
+Mailcow does not use any cross site scripts, or documents. Thus, you should set CORP and COOP headers to their strictest configuration:
+
+```
+add_header Cross-Origin-Opener-Policy same-origin;
+add_header Cross-Origin-Resource-Policy same-origin;
+```
+
+If you do not use Gravatar with SOGo, you can also set COEP to require-corp since image embedding will not be used either:
+
+```
+add_header Cross-Origin-Embedder-Policy require-corp;
+```
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