GetGrav up to 2.0.20 Admin tHtml Username cross site scripting

Summaryinfo

A vulnerability marked as problematic has been reported in GetGrav Grav up to 2.0.20. Affected by this issue is the function tHtml of the component Admin. This manipulation of the argument Username causes cross site scripting. This vulnerability appears as CVE-2026-85600. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability classified as problematic was found in GetGrav Grav up to 2.0.20. Affected by this vulnerability is the function tHtml of the component Admin. The manipulation of the argument username with an unknown input leads to a cross site scripting vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect integrity. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-85600 since 09/04/2026. The exploitation appears to be easy. The attack can be launched remotely. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

Upgrading to version 2.0.21 eliminates this vulnerability.

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Productinfo

Vendor

• GetGrav

Name

• Grav

Version

• 2.0.0
• 2.0.1
• 2.0.2
• 2.0.3
• 2.0.4
• 2.0.5
• 2.0.6
• 2.0.7
• 2.0.8
• 2.0.9
• 2.0.10
• 2.0.11
• 2.0.12
• 2.0.13
• 2.0.14
• 2.0.15
• 2.0.16
• 2.0.17
• 2.0.18
• 2.0.19
• 2.0.20

Website

• Product: https://github.com/getgrav/grav/

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