CVE-2026-75834 Grav before 2.0.14 Stored XSS via Invalid UTF-8 Byte
An authenticated attacker can store malicious JavaScript in Grav CMS pages by bypassing XSS filters with invalid UTF-8 bytes, leading to execution in visitors' browsers.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-75834?
CVE-2026-75834 is a medium-severity cross-site scripting vulnerability in getgrav grav, published on 18 Aug 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Grav before 2.0.14 contains a stored cross-site scripting vulnerability in the Security::detectXss() function (system/src/Grav/Common/Security.php). All XSS detection patterns use the PCRE /u (UTF-8) modifier, so a single invalid UTF-8 byte anywhere in page content causes preg_match() to return false for every pattern, silently bypassing the save-time XSS safety gate (Validation::checkSafety()). An authenticated attacker with page-edit permissions (without the security.xss_whitelist privilege) can store malicious JavaScript that executes in the browser of a visitor who views the affected page.
Weakness: CWE-79
Which versions are affected by CVE-2026-75834?
2 open source packages ship an affected version, including getgrav/grav.
| Package | Affected | Fixed in |
|---|---|---|
getgrav/grav Packagist | All versions | 2.0.14 |
getgrav/grav Packagist | All versions | 2.0.14 |
How do I fix CVE-2026-75834?
Upgrade getgrav/grav to 2.0.14 or later.
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-2026-75834 being exploited?
There is no known exploitation of CVE-2026-75834 in the wild and no public exploit code.
Sources
Also known as GHSA-q2j8-x8hf-63ch.