Description
Improper neutralization of input in Checkmk versions 2.4.0 before 2.4.0p22, and 2.3.0 before 2.3.0p43 allows an attacker that can manipulate a host's check output to inject malicious JavaScript into the Synthetic Monitoring HTML logs, which can then be accessed via a crafted phishing link.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Checkmk | Checkmk | 2.4.0 – < 2.4.0p22, 2.3.0 – < 2.3.0p43 | 2.4.0p22 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | check-mk | No fix yet | — |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 16.04 LTS | check-mk | No fix yet | — |
Advisories 1
- WID-SEC-2026-0543 Checkmk: Schwachstelle ermöglicht Cross-Site Scripting BSI CERT-Bund (WID) · Feb 26, 2026