CVE-2026-25199: Instances deployed via the Proxmox extension allow unauthorized access to instances belonging to other tenants

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CRITICAL 9.1REMOTEWATCHLISTUPGRADE

CVE-2026-25199 is a critical-severity flaw (CVSS 9.1) affecting cloudstack. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Instances deployed via the Proxmox extension allow unauthorized access to instances belonging to other tenants. This issue affects Apache CloudStack: from 4.21.0.0 through 4.22.0.0. The Proxmox extension for CloudStack improperly uses a user-editable instance setting, proxmox_vmid, to associate CloudStack instances with Proxmox virtual machines. Because this value is not restricted or validated against tenant ownership and Proxmox VM IDs

Why this priority

Critical severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-200
Published	2026-05-08
Last modified	2026-10-26

Publisher (CNA): Apache Software Foundation · Vendor: apache

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

Am I affected?

Timeline

2026-05-08 13:16 UTCPublished CVE record published
2026-10-26 19:10 UTCUpdated Record last modified

apache cloudstack UPGRADE

Affected: >= 4.21.0.0 and < 4.22.0.1

Fixed in: 4.22.0.1

Safe to downgrade to: a release before 4.21.0.0

1. Check installed version

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

2. UPGRADE to 4.22.0.1 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade cloudstack

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 4.21.0.0 (Debian / Ubuntu)

apt-cache madison cloudstack sudo apt install cloudstack=<VERSION_BEFORE_4.21.0.0> sudo apt-mark hold cloudstack

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

dnf --showduplicates list cloudstack sudo dnf downgrade cloudstack-<VERSION_BEFORE_4.21.0.0> sudo dnf versionlock add cloudstack

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-2026-25199?

cloudstack: upgrade to 4.22.0.1. Exact commands for each OS are on this page.

Is CVE-2026-25199 being exploited?

CVE-2026-25199 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-2026-25199 affect?

CVE-2026-25199 affects cloudstack. Severity is critical (CVSS 9.1). Instances deployed via the Proxmox extension allow unauthorized access to instances belonging to other tenants. This issue affects Apache CloudStack: from 4.21.0.0 through 4.22.0.0. The Proxmox extension for CloudStack improperly us

How urgent is CVE-2026-25199?

Priority 52/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Proxmox vulnerabilities

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References

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