CVE-2026-34090: Exposure of Sensitive Information to an Unauthorized Actor vulnerability in Wikimedia Foundation CheckUser. T

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-34090 is a high-severity flaw (CVSS 7.5) affecting checkuser. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Exposure of Sensitive Information to an Unauthorized Actor vulnerability in Wikimedia Foundation CheckUser. This issue affects CheckUser: from 1.45.0 before 1.45.2.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-200
Published	2026-05-11
Last modified	2026-10-26

Publisher (CNA): wikimedia-foundation · Vendor: mediawiki

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-11 16:17 UTCPublished CVE record published
2026-10-26 18:10 UTCUpdated Record last modified

mediawiki checkuser UPGRADE

Affected: >= 1.45.0 and < 1.45.2

Fixed in: 1.45.2

Safe to downgrade to: a release before 1.45.0

1. Check installed version

apt-cache policy checkuser || rpm -q checkuser || checkuser --version

2. UPGRADE to 1.45.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade checkuser

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade checkuser

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.45.0 (Debian / Ubuntu)

apt-cache madison checkuser sudo apt install checkuser=<VERSION_BEFORE_1.45.0> sudo apt-mark hold checkuser

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list checkuser sudo dnf downgrade checkuser-<VERSION_BEFORE_1.45.0> sudo dnf versionlock add checkuser

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-2026-34090?

checkuser: upgrade to 1.45.2. Exact commands for each OS are on this page.

Is CVE-2026-34090 being exploited?

CVE-2026-34090 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-2026-34090 affect?

CVE-2026-34090 affects checkuser. Severity is high (CVSS 7.5). Exposure of Sensitive Information to an Unauthorized Actor vulnerability in Wikimedia Foundation CheckUser. This issue affects CheckUser: from 1.45.0 before 1.45.2.

How urgent is CVE-2026-34090?

Priority 36/100. High severity; Remotely exploitable, no login, no user action

References

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