CVE-2026-104021 Code injection in Fastcache by Host.it
Authenticated administrators can inject arbitrary Apache directives into .htaccess to execute remote PHP code on the server.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-104021?
CVE-2026-104021 is a high-severity code injection vulnerability in hostspa Fastcache by Host.it, published on 10 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
The Fastcache by Host.it plugin for WordPress is vulnerable to Code Injection in all versions up to, and including, 1.7.4 via the `fastcache_settings[cache_cookie_exclude][]` parameter. This is due to the plugin registering the `cache_cookie_exclude` setting via `register_setting()` without a `sanitize_callback`, while `buildSiteHtaccessRules()` applies only `trim()` to each cookie value before interpolating it directly into an Apache `RewriteCond` line — a normalization that strips surrounding whitespace but leaves embedded newlines intact, allowing an attacker to break out of the capture group and append arbitrary directives. This makes it possible for authenticated attackers, with administrator-level access and above, to inject arbitrary Apache directives into the site's `.htaccess` file via `file_put_contents()`, enabling server-level configuration changes such as setting `php_value auto_prepend_file` to execute attacker-controlled PHP code on every request.
Weakness: CWE-94
Which versions are affected by CVE-2026-104021?
How do I fix CVE-2026-104021?
No fix has been published for CVE-2026-104021 yet. Limit exposure of the affected software until one is available.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-104021 being exploited?
There is no known exploitation of CVE-2026-104021 in the wild and no public exploit code.
Sources
Also known as GHSA-hm53-mjmf-w6v4.