LibreNMS Alert Rule API Cross-Site Scripting Vulnerability

Please find POC file here https://trendmicro-my.sharepoint.com/:u:/p/kholoud_altookhy/IQCfcnOE5ykQSb6Fm-HFI872AZ_zeIJxU-3aDk0jh_eX_NE?e=zkN76d

ZDI-CAN-28575: LibreNMS Alert Rule API Cross-Site Scripting Vulnerability

-- CVSS -----------------------------------------

4.3: AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:L/A:L

-- ABSTRACT -------------------------------------

Trend Micro's Zero Day Initiative has identified a vulnerability affecting the following products: LibreNMS - LibreNMS

-- VULNERABILITY DETAILS ------------------------

• Version tested: 25.10.0
• Installer file: NA
• Platform tested: NA

Analysis

LibreNMS Alert Rule API Stored Cross-Site Scripting

Overview

Alert rules can be created or updated via LibreNMS API. The alert rule name is not properly sanitized, and can be used to inject HTML code.

Affected versions

The latest version at the time of writing (25.10.0) is vulnerable.

Root cause

When an alert rule is created or updated via the API, function add_edit_rule() in includes/html/api_functions.inc.php is called to add/update the entry in the database. When an alert rule is created via the web interface, HTML tags are stripped from the rule name, however this is not the case when using the API.

As such, it is possible to create an alert rule where the name is:

<script>alert(1)</script>

Later, when a victim browses to the Alerts > Alert Rule page, PHP script\xc2\xa0includes/html/print-alert/rules.php\xc2\xa0is called. It notably includes the file\xc2\xa0includes/html/modal/alert_rule_list.inc.php, which returns HTML code for a modal window that searches alert rules.

The modal window includes an HTML table with all rules, including their name, and an inline JavaScript that calls the\xc2\xa0bootgrid()\xc2\xa0function (http://www.jquery-bootgrid.com/) for styling and enhancing the table.

alert_rule.list.inc.php sanitizes the rule name with the function e() before including it in the table, which XML encodes all special characters. However the\xc2\xa0bootgrid()\xc2\xa0function rewrites the table cells content when enhancing the table, and as a side effect, XML character references are decoded. After the script updated the table, the browser now interprets the payload as HTML tags and includes the code to the DOM.

Detection guidance

• inspect HTTP POST and PUT requests to a Request-URI that includes the string\xc2\xa0/api/v0/rules
• check if the\xc2\xa0name\xc2\xa0JSON value includes a < character

PoC

The proof-of-concept can be run as such:

python3 poc.py ip_addr -T <token>

-- CREDIT --------------------------------------- This vulnerability was discovered by: Simon Humbert of Trend Research of Trend Micro

-- FURTHER DETAILS ------------------------------

Supporting files:

If supporting files were contained with this report they are provided within a password protected ZIP file. The password is the ZDI candidate number in the form: ZDI-CAN-XXXX where XXXX is the ID number.

Please confirm receipt of this report. We expect all vendors to remediate ZDI vulnerabilities within 120 days of the reported date. If you are ready to release a patch at any point leading up to the deadline, please coordinate with us so that we may release our advisory detailing the issue. If the 120-day deadline is reached and no patch has been made available we will release a limited public advisory with our own mitigations, so that the public can protect themselves in the absence of a patch. Please keep us updated regarding the status of this issue and feel free to contact us at any time:

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