CVE-2026-31834 — Umbraco.Cms
HIGHCVE-2026-31834 is a high-severity (CVSS 7.2) Improper Privilege Management vulnerability in Umbraco.Cms. A fix is available for Umbraco.Cms — see the affected versions and patch details below.
Umbraco Affected by Vertical Privilege Escalation via Missing Authorization Checks
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-31834.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
Umbraco.Cms.NETUmbraco.CmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Description
A privilege escalation vulnerability has been identified in Umbraco CMS. Under certain conditions, authenticated backoffice users with permission to manage users, may be able to elevate their privileges due to insufficient authorization enforcement when modifying user group memberships.
The affected functionality does not properly validate whether a user has sufficient privileges to assign highly privileged roles.
Impact
An authenticated backoffice user may be able to escalate their privileges to Administrator level.
Successful exploitation results in full administrative control of the affected Umbraco CMS instance, including unrestricted access to content, user management, and configuration settings.
The impact is significantly mitigated by the fact that this can only be exploited by a user that has already been given access to the "Users" section in the CMS. For most Umbraco setups, such users are already also "Administrators".
Patches
The issue is patched in 16.5.1 and 17.2.2.
Workarounds
There is no workaround other than upgrading for setups where they want to have users with permission for the "Users" section without also being content with those users also being part of the "Administrators" user group.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Umbraco.Cms | ≥ 15.3.1&&< 16.5.1 | 16.5.1dotnet add package Umbraco.Cms --version 16.5.1 |
| .NETNuGet | Umbraco.Cms | ≥ 17.0.0&&< 17.2.2 | 17.2.2dotnet add package Umbraco.Cms --version 17.2.2 |
Affected Products
umbraco cmsumbracoDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Umbraco.Cms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Umbraco.Cms to 16.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-31834 is resolved across your whole dependency graph.
Workarounds
Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.
Frequently Asked Questions
Is CVE-2026-31834 in your dependencies?
Find it across NuGet, including transitive dependencies.