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MEDIUM severity

CVE-2021-38156 — Nagios Xi

MEDIUM

CVE-2021-38156 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in nagios nagios xi. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available — see the affected versions and patch details below.

In Nagios XI before 5.8.6, XSS exists in the dashboard page (/dashboards/#) when administrative users attempt to edit a dashboard.

Published
Updated
Affected
1 product
Patched
See advisory
Exploits
1 known
Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
92.9%probability of exploitation in next 30 days
Very High Risk0.00%
Lower risk than most CVEs100th percentile — riskier than 100% of all scored CVEsHighest risk
81.3%86.1%90.8%95.6%84.0%92.9%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Description

In Nagios XI before 5.8.6, XSS exists in the dashboard page (/dashboards/#) when administrative users attempt to edit a dashboard.

Affected Products

1 product · 1 configurations
Application
nagios xinagios
< 5.8.6
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

In Nagios XI before 5.8.6, XSS exists in the dashboard page (/dashboards…

raxis.comNVDSep 2021

Detection & mitigation playbook

Vendor / appliance

  1. Detect

    Inventory every nagios nagios xi deployment and check each version against the affected-products list above.

  2. Fix

    Apply the nagios nagios xi security patch or hotfix for CVE-2021-38156 on the affected version, following the vendor advisory for your exact build.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

How to detect CVE-2021-38156

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2021-38156 -u https://target
Template
Nagios XI < 5.8.6 - Cross-Site Scripting
Severity
medium
Impact
Authenticated attackers can inject malicious JavaScript via XSS in the dashboard title field, potentially stealing administrator session cookies or performing administrative actions.
Remediation
Upgrade to Nagios XI version 5.8.6 or later.

Template by ProjectDiscovery nuclei-templates (ritikchaddha), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

In Nagios XI before 5.8.6, XSS exists in the dashboard page (/dashboards/#) when administrative users attempt to edit a dashboard.
O3 Security · Runtime Protection

Is CVE-2021-38156 being exploited in your environment?

Detect and block the exploit chain at execution, on systems you cannot patch yet.

Protect my workloads How runtime protection works
CVE-2021-38156: Nagios Xi XSS (Medium 5.4)