Description
A cross site scripting (XSS) vulnerability exists in Check_MK versions 1.4.0x prior to 1.4.0p6, allowing an unauthenticated remote attacker to inject arbitrary HTML or JavaScript via the _username parameter when attempting authentication to webapi.py, which is returned unencoded with content type text/html.
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 | 1.2.8p16-1ubuntu0.2 | USN-5527-1 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 16.04 LTS | check-mk | 1.2.6p12-1ubuntu0.16.04.1+esm1 | USN-5527-2 |
Advisories 2
- USN-5527-2 check-mk vulnerabilities Ubuntu Security Notices (USN) · Jun 25, 2026
- USN-5527-1 check-mk vulnerabilities Ubuntu Security Notices (USN) · Feb 10, 2026