Description
Improper neutralization of HTML-encoded characters in the URL validation function in Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions allows an authenticated user to bypass URL validation and inject malicious URLs such as javascript: URIs, resulting in cross-site scripting when another user interacts with the crafted link.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Checkmk | Checkmk | 2.5.0 – < 2.5.0p5, 2.4.0 – < 2.4.0p31, 2.3.0 – < 2.3.0p48, 2.2.0 | 2.5.0p5 |
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-2026-1817 Checkmk: Mehrere Schwachstellen ermöglichen Cross-Site Scripting BSI CERT-Bund (WID) · Jun 8, 2026
References
- https://checkmk.com/werk/20002 vendor-advisory