5.4

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2021-27131

CVE-2021-27131: Moodle vulnerable to stored Cross-site Scripting

Moodle 3.10.1 is vulnerable to persistent/stored cross-site scripting (XSS) due to the improper input sanitization on the "Additional HTML Section" via "Header and Footer" parameter in /admin/settings.php. This vulnerability may lead an attacker to steal admin and all user account cookies by storing the malicious XSS payload in Header and Footer.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2021-27131

CVE-2021-27131:

5.4

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
moodle/moodle	composer	<= 3.10.1

Technical Details

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Miggo AI

Root Cause Analysis

The vulnerability stems from improper sanitization of admin-provided HTML in header/footer settings. Moodle's admin settings typically use admin_setting_configtextarea which accepts PARAM_RAW (raw text input). While admins are permitted to add custom HTML/JS, the vulnerability arises when this content is rendered without context-aware escaping in page templates. The combination of PARAM_RAW input handling in admin settings and lack of output encoding in template rendering creates the XSS vector. The disputed nature by the vendor confirms this is an intentional admin capability, but the CVE argues it's a vulnerability when admin-compromised accounts inject malicious scripts affecting other users.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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