CVE-2026-85600
Received Received - Intake

Stored XSS in Grav Admin Plugin

Publication date: 2026-09-04

Last updated on: 2026-09-04

Assigner: VulnCheck

Description
Grav Admin (getgrav/grav-plugin-admin2) versions <= 2.0.19 contain a stored cross-site scripting vulnerability in the tHtml() function (src/lib/stores/i18n.svelte.ts), which substitutes untrusted parameters such as usernames into translation templates before parsing the result as markdown. Grav's server-side username validation (DataUser::isValidUsername) blocks filesystem-dangerous characters but not <, >, ", or ', allowing an attacker to register a username containing an HTML payload. When an administrator views a UI surface that renders the username through tHtml()—such as the two-factor force-disable confirmation prompt or the 'page is locked' editor notice—the payload executes in their authenticated session. Fixed in 2.0.21.

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Meta Information

Published
2026-09-04
Last Modified
2026-09-04
Generated
2026-09-04
AI Q&A
2026-09-04
EPSS Evaluated
N/A
NVD
CVE-2026-85600
EUVD
EUVD-2026-71023

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
getgrav grav-plugin-admin2 to 2.0.19 (inc)
getgrav grav-plugin-admin2 2.0.21

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.

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Executive Summary

This is a stored cross-site scripting (XSS) vulnerability in Grav Admin versions before 2.0.21. It occurs in the tHtml() function where untrusted parameters like usernames are inserted into translation templates before being parsed as markdown. The server-side username validation fails to block HTML metacharacters such as <, >, ", or ', allowing attackers to register malicious usernames with HTML payloads. When administrators view affected UI surfaces, the payload executes in their authenticated session.

Detection Guidance

To detect this vulnerability, check if Grav Admin versions are below 2.0.21. Inspect the file src/lib/stores/i18n.svelte.ts for the tHtml() function usage. Look for usernames containing HTML payloads like <img src=x onerror=alert(1)> in admin interfaces.

Impact Analysis

An attacker could execute arbitrary JavaScript in an administrator's session, leading to account takeover or further exploitation. The impact includes potential unauthorized access to sensitive data, manipulation of admin interfaces, or installation of additional malicious code. The vulnerability is exploitable by low-privileged users if self-registration is enabled, making it accessible even to unauthenticated attackers.

Compliance Impact

This vulnerability could lead to unauthorized access to personal or sensitive data, violating GDPR's data protection principles and HIPAA's security requirements. It may result in data breaches, unauthorized modifications, or disclosure of protected health information, potentially leading to legal penalties and reputational damage.

Mitigation Strategies

Immediately update Grav Admin to version 2.0.21 or later. If updating is not possible, restrict username input to block HTML metacharacters like <, >, ", and '. Disable self-registration if enabled to prevent unauthenticated exploitation.

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