CVE-2026-31832 — Umbraco.Cms
MEDIUMCVE-2026-31832 is a medium-severity (CVSS 5.4) CWE-639 vulnerability in Umbraco.Cms. A fix is available for Umbraco.Cms — see the affected versions and patch details below.
Umbraco Backoffice API Allows Unauthorized Modification of Domain Data
Exploitation Status
No confirmed exploitation observed yet
- 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-2026-31832.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-31832 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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 broken object-level authorization vulnerability exists in a backoffice API endpoint that allows authenticated users to assign domain-related data to content nodes without proper authorization checks.
The issue is caused by insufficient authorization enforcement on the affected API endpoint, whereby via an API call, domains can be set on content nodes that the editor does not have permission to access (either via user group privileges or start nodes).
Impact
An attacker can modify domain configurations for content nodes they are not permitted to edit. This may result in malicious or unintended routing behaviour, service disruption, and potential disclosure of configuration-related information.
Patches
The issue is patched in 16.5.1 and 17.2.2.
Workarounds
There is no workaround other than upgrading.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Umbraco.Cms | ≥ 14.0.0&&< 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 |
Detection & 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-2026-31832 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-31832 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-31832. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-31832 in your dependencies?
O3 Security finds CVE-2026-31832 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.