CVE-2021-4072: XSS in elgg Social Network Platform

Successful exploitation of CVE-2021-4072 allows an attacker to execute arbitrary JavaScript code within the context of a victim's browser. This can be leveraged to steal session cookies, redirect users to malicious websites, deface the elgg instance, or even gain complete control over user accounts. The impact is particularly severe because elgg is often used in environments where sensitive user data is stored and processed, such as educational institutions and community organizations. The attacker could potentially gain access to private messages, personal information, and other sensitive data stored within the elgg system. This vulnerability shares similarities with other XSS vulnerabilities, where improper input sanitization leads to the execution of attacker-controlled code.

1. Reserved2021-12-06
2. Published2021-12-24
3. Modified2024-08-03
4. EPSS updated2026-04-02

The primary mitigation for CVE-2021-4072 is to immediately upgrade elgg to version 3.3.24 or later. If upgrading is not immediately feasible, consider implementing input validation and output encoding on all user-supplied data to prevent the injection of malicious scripts. Web Application Firewalls (WAFs) can be configured to filter out potentially malicious requests containing XSS payloads. Regularly review and update elgg's configuration to ensure that all security settings are properly configured. After upgrading, confirm the fix by attempting to inject a simple XSS payload (e.g., <script>alert('XSS')</script>) into a form field and verifying that the script is not executed.