Fix the malformed Strict-Transport-Security header on Apache

Why it matters

The header is present but does not follow the required syntax, so browsers ignore it and your site gets no HSTS protection. A small typo such as a missing max-age is enough.

Staged change. Do this in stages and check each one before the next, so a mistake does not break your site or your mail.

The fix

1. Search for the header (grep -R Strict-Transport-Security /etc/apache2 /var/www/.htaccess) and keep one correct line. Use Header always set everywhere, never append or add. A plain Header set elsewhere (for example in .htaccess) is a separate table in Apache and can leave two headers on the response.
2. Run apachectl configtest and reload.

Header always set Strict-Transport-Security "max-age=300"

Read the documentation ↗(opens in a new tab)

Related

• Reported by the HSTS check
• Add the Strict-Transport-Security (HSTS) header
• Re-enable HSTS (max-age is zero)
• Raise the HSTS max-age
• Decide whether to add includeSubDomains
• Meet the HSTS preload requirements or remove preload
• Consider submitting the domain to the HSTS preload list