CVE-2026-45286: Nextcloud is an open source content collaboration platform

Routine

MEDIUM 4.3UPGRADE

CVE-2026-45286 is a medium-severity flaw (CVSS 4.3) affecting calendar. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Nextcloud is an open source content collaboration platform. From versions 5.5.13 to before 5.5.17, and 6.2.0 to before 6.2.3, an authenticated user can enumerate users on the same Nextcloud instance by using the Calendar app's endpoint for suggesting attendees. The sharing restrictions, applied to other endpoints, were not effective here. This issue has been patched in versions 5.5.17 and 6.2.3.

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-200
Published	2026-06-01
Last modified	2026-07-22

Publisher (CNA): GitHub, Inc. · Vendor: nextcloud

Last updated 2026-07-22 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-01 19:16 UTCPublished CVE record published
2026-07-22 08:10 UTCUpdated Record last modified

nextcloud calendar UPGRADE

Affected: >= 5.5.13 and < 5.5.17 · >= 6.2.0 and < 6.2.3

Fixed in: 5.5.17, 6.2.3

Safe to downgrade to: a release before 5.5.13

1. Check installed version

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

2. UPGRADE to 5.5.17 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade calendar

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 5.5.13 (Debian / Ubuntu)

apt-cache madison calendar sudo apt install calendar=<VERSION_BEFORE_5.5.13> sudo apt-mark hold calendar

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

dnf --showduplicates list calendar sudo dnf downgrade calendar-<VERSION_BEFORE_5.5.13> sudo dnf versionlock add calendar

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-2026-45286?

calendar: upgrade to 5.5.17, 6.2.3. Exact commands for each OS are on this page.

Is CVE-2026-45286 being exploited?

CVE-2026-45286 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-2026-45286 affect?

CVE-2026-45286 affects calendar. Severity is medium (CVSS 4.3). Nextcloud is an open source content collaboration platform. From versions 5.5.13 to before 5.5.17, and 6.2.0 to before 6.2.3, an authenticated user can enumerate users on the same Nextcloud instance by using the Calendar app's endpoint for

How urgent is CVE-2026-45286?

Priority 25/100. Public exploit reference

Software pages

Nextcloud vulnerabilities

References

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