How to fix missing strict transport security on Squarespace

Steps for Squarespace

1. Squarespace handles all SSL and security headers at the infrastructure level; individual header values are not configurable via the Squarespace dashboard.
2. Confirm your domain has SSL enabled: Squarespace Admin → Settings → Domains → your domain should show a green lock / 'SSL Active'.
3. Squarespace enables HSTS for all sites on its platform. If a scanner flags the header as missing on your Squarespace site, it may be scanning an HTTP URL before the redirect — test the HTTPS version directly.
4. If you proxy Squarespace through Cloudflare, add HSTS in Cloudflare: SSL/TLS → Edge Certificates → HSTS → Enable, Max-Age 1 year, Include Subdomains.

Strict-Transport-Security: max-age=31536000; includeSubDomains

What is missing strict transport security?

HTTP Strict-Transport-Security (HSTS) is a security header your web server sends to browsers to say: "Always use HTTPS when talking to this site — never plain HTTP." Once a browser sees this header, it will automatically upgrade any future HTTP requests to HTTPS for the duration you specify (the `max-age`, measured in seconds). Without it, a visitor who types your domain or follows an old HTTP link could briefly connect over an unencrypted connection before being redirected, which is a window an attacker can exploit.

Without HSTS, your store is vulnerable to SSL-stripping attacks, where an attacker on the same network (e.g., a coffee shop Wi-Fi) intercepts the first unencrypted HTTP request before your redirect kicks in, silently reading or tampering with the connection. This can expose customer login credentials, payment data, and session cookies — creating serious legal risk under GDPR, CCPA, and PCI-DSS. Google also uses HTTPS as a ranking signal; a missing HSTS header signals an incomplete security posture that can reduce trust scores. Perhaps most directly, browsers increasingly warn users about mixed or insecure connections, and a visible browser security warning will kill conversions instantly.

See the complete Missing strict transport security guide for every platform and the full background.