What is CVE-2021-38156?

CVE-2021-38156 is a medium-severity vulnerability in Nagios Xi, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-09-15.

How severe is CVE-2021-38156?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Is CVE-2021-38156 known to be exploited?

5 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in Nagios Xi

CVE-2021-38156

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

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-09-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.929 (99.8th percentile), scored 2026-10-19.

High probability of exploitation in the next 30 days — patch promptly. 100th percentile — 99.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.929 · newest: 0.929 · change: 0.000

Affected products

Nagios Xi

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

References

www.nagios.com/downloads/nagios-xi/change-log/ (Release Notes, Vendor Advisory)
raxis.com/blog/cve-2021-38156 (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-38156?: CVE-2021-38156 is a medium-severity vulnerability in Nagios Xi, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-09-15.
How severe is CVE-2021-38156?: Medium severity. CVSS v3 base score is 5.4 out of 10.
Is CVE-2021-38156 known to be exploited?: 5 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.