CVE-2026-75834
Received Received - Intake

Stored XSS in Grav CMS Prior to 2.0.14

Publication date: 2026-08-18

Last updated on: 2026-08-18

Assigner: VulnCheck

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.

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Meta Information

Published
2026-08-18
Last Modified
2026-08-18
Generated
2026-08-18
AI Q&A
2026-08-18
EPSS Evaluated
N/A
NVD
CVE-2026-75834
EUVD
EUVD-2026-60598

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
getgrav grav to 2.0.14 (exc)
grav grav to 2.0.14 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Attack-Flow Graph

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Executive Summary

This is a stored cross-site scripting (XSS) vulnerability in Grav versions before 2.0.14. It occurs because the Security::detectXss() function uses PCRE regex patterns with the UTF-8 modifier (/u). A single invalid UTF-8 byte in user input causes preg_match() to return false for all patterns, bypassing XSS detection during content saving. An attacker with page-edit permissions can inject malicious JavaScript that executes when other users view the page.

Detection Guidance

Check Grav version with 'bin/grav version' and compare against 2.0.14. Inspect system/src/Grav/Common/Security.php for the Security::detectXss() function implementation. Review logs for unusual page edits or XSS-related errors.

Impact Analysis

An authenticated attacker with page-edit permissions can store malicious JavaScript on a Grav page. When other users, including administrators, view the affected page, the injected script executes in their browsers. This could lead to session hijacking, data theft, or unauthorized actions performed on behalf of the user.

Compliance Impact

This vulnerability could lead to unauthorized access to user data, violating GDPR's data protection principles and HIPAA's security requirements for protected health information. Organizations using vulnerable Grav versions may face compliance violations, legal liabilities, and reputational damage if exploited.

Mitigation Strategies

Upgrade Grav to version 2.0.14 or later immediately. If upgrading is not possible, review and restrict page-edit permissions to trusted users only. Monitor for suspicious page edits and implement additional input validation for UTF-8 encoding.

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