CVE-2026-33406 Pi-hole has a Stored HTML attribute injection

Medium 5.4 Published 6 Apr 2026 Updated 7 Apr 2026

Attackers can inject HTML attributes via malicious backups to alter UI styling, bypassing CSP restrictions in the Pi-hole admin interface.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2026-33406?

CVE-2026-33406 is a medium-severity cross-site scripting vulnerability in pi-hole web, published on 6 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

Pi-hole Admin Interface is a web interface for managing Pi-hole, a network-level ad and internet tracker blocking application. From 6.0 to before 6.5, configuration values from the /api/config endpoint are placed directly into HTML value="" attributes without escaping in settings-advanced.js, enabling HTML attribute injection. A double quote in any config value breaks out of the attribute context. JavaScript execution is blocked by the server's CSP (script-src 'self'), but injected attributes can alter element styling for UI redressing. The primary attack vector is importing a malicious teleporter backup, which bypasses per-field server-side validation. This vulnerability is fixed in 6.5.

Weakness: CWE-79

Which versions are affected by CVE-2026-33406?

It affects 1 product.

Products include Pi-Hole Web Interface.

How do I fix CVE-2026-33406?

No fix has been published for CVE-2026-33406 yet. Limit exposure of the affected software until one is available.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2026-33406 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33406 exists.

Sources

Also known as GHSA-9rfm-c5g6-538p.