CVE-2017-9781: A cross site scripting (XSS) vulnerability exists in Check_MK versions 1.4.0x prior to 1.4.0p6, allowing an un

This month

MEDIUM 6.1DOWNGRADE

CVE-2017-9781 is a medium-severity flaw (CVSS 6.1) affecting check mk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.4% (top 27%)
CISA exploited list	No
Weakness	CWE-79
Published	2017-06-21
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: check mk project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2017-06-21 18:29 UTCPublished CVE record published
2026-06-17 01:28 UTCUpdated Record last modified

check mk project check mk DOWNGRADE

Affected: 1.4.0 · 1.4.0 p1 · 1.4.0 p2 · 1.4.0 p3 · 1.4.0 p4 · 1.4.0 p5

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.4.0

1. Check installed version

apt-cache policy check-mk || rpm -q check-mk || check-mk --version

2. No fixed release: DOWNGRADE to a release before 1.4.0 (Debian / Ubuntu)

apt-cache madison check-mk sudo apt install check-mk=<VERSION_BEFORE_1.4.0> sudo apt-mark hold check-mk

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list check-mk sudo dnf downgrade check-mk-<VERSION_BEFORE_1.4.0> sudo dnf versionlock add check-mk

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2017-9781?

check mk: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2017-9781 being exploited?

CVE-2017-9781 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2017-9781 affect?

CVE-2017-9781 affects check mk. Severity is medium (CVSS 6.1). 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

How urgent is CVE-2017-9781?

Priority 45/100. Public exploit reference

Related CVEs

CVE-2017-11507 MEDIUM 6.1 DOWNGRADE A cross site scripting (XSS) vulnerability exists in Check_MK versions 1.2.8x prior to 1.2.8p25 and 1.4.0x pri
CVE-2014-0243 MEDIUM 5.5 UPGRADE Check_MK through 1.2.5i2p1 allows local users to read arbitrary files via a symlink attack to a file in /var/l

References

← Back to latest CVEs