CVE-2026-102586: Moodle Password Reset XSS Vulnerability

CVE-2026-102586 Overview

A cross-site scripting (XSS) vulnerability affects Moodle's password reset page. The flaw stems from insufficient sanitization of the username input field. A remote attacker can craft a malicious password reset link and convince an unauthenticated user to visit it. When the victim loads the link, arbitrary JavaScript executes in their browser context. The issue is classified under CWE-79: Improper Neutralization of Input During Web Page Generation. Exploitation requires user interaction but no authentication or elevated privileges.

Critical Impact
An attacker can execute arbitrary script in a victim's browser session, enabling credential theft, session hijacking, or redirection to attacker-controlled infrastructure.

Affected Products

Moodle Learning Management System (specific affected versions not enumerated in NVD)
Red Hat distributions packaging Moodle (see Red Hat CVE-2026-102586)
Any deployment exposing the Moodle password reset page to untrusted networks

Discovery Timeline

2026-09-30 - CVE CVE-2026-102586 published to NVD
2026-09-30 - Last updated in NVD database

Technical Details for CVE-2026-102586

Vulnerability Analysis

The vulnerability resides in Moodle's password reset workflow. The page accepts a username parameter from the request and renders it back into the HTML response. Because the input is not properly sanitized or contextually encoded, attacker-supplied markup and script content survive to the rendered page. When a victim opens a crafted URL, the injected payload executes in the origin of the Moodle site. The attack requires user interaction: the victim must click the malicious link. No authentication is required, and the attack traverses the network. Refer to the Moodle Forum Discussion and Red Hat Bug 2543641 for additional context.

Root Cause

The password reset handler fails to apply output encoding to the username value before including it in the HTML response. Moodle's standard sanitization helpers were not applied to this specific input path. This is a classic reflected XSS pattern under [CWE-79].

Attack Vector

An attacker constructs a URL to the Moodle password reset endpoint that embeds a JavaScript payload within the username parameter. The attacker delivers the URL through phishing email, social media, or a compromised web page. When the victim clicks the link, the Moodle server reflects the payload into the response and the browser executes it. The payload can exfiltrate cookies, submit forms on behalf of the user, or pivot to further attacks against the Moodle session.

No verified proof-of-concept code has been published. See the upstream fix referenced in the Moodle Commit MDL-88335 for the sanitization change.

Detection Methods for CVE-2026-102586

Indicators of Compromise

Web server or reverse proxy access logs showing requests to the password reset endpoint containing URL-encoded characters such as %3Cscript%3E, onerror=, javascript:, or other HTML/JS syntax in the username parameter.
Referrer headers on password reset requests originating from unfamiliar external domains, phishing infrastructure, or URL shortening services.
Unexpected outbound requests from user browsers to attacker-controlled hosts immediately after a password reset page visit.

Detection Strategies

Deploy web application firewall (WAF) rules that inspect the username parameter on the password reset URL for HTML tags, event handlers, and script keywords.
Enable Content Security Policy (CSP) reporting to capture blocked inline script executions on password reset pages.
Correlate password reset page requests with subsequent anomalous authentication events or account changes in the same session.

Monitoring Recommendations

Alert on any password reset URL containing angle brackets, quotes, or common XSS keywords in query parameters.
Monitor Moodle application logs for spikes in password reset requests from single source addresses.
Review outbound egress logs from user workstations for connections to newly registered domains following Moodle interactions.

How to Mitigate CVE-2026-102586

Immediate Actions Required

Apply the upstream Moodle patch referenced in Moodle Commit MDL-88335 as soon as your maintenance window permits.
For Red Hat–packaged deployments, track the vendor advisory at Red Hat CVE-2026-102586 and install updated packages when available.
Notify users to avoid clicking password reset links received from untrusted sources or unsolicited messages.

Patch Information

The fix is tracked in the Moodle issue tracker as MDL-88335 and applied through the corresponding commit in the Moodle Git repository. Administrators should upgrade to the Moodle minor release that includes this commit. Red Hat customers should monitor Red Hat Bug 2543641 for downstream package updates.

Workarounds

Enforce a strict Content Security Policy on the Moodle site that disallows inline scripts and restricts script sources to trusted origins.
Deploy WAF signatures that block HTML and JavaScript syntax in the username parameter of the password reset endpoint.
Restrict access to the password reset page behind an authenticated portal or CAPTCHA to reduce exposure to unauthenticated attackers.

bash

# Example NGINX rule blocking obvious XSS payloads on the password reset path
location /login/forgot_password.php {
    if ($arg_username ~* "(<|>|script|onerror|onload|javascript:)") {
        return 403;
    }
    proxy_pass http://moodle_backend;
}