Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
Umbraco.Cms versions from 15.3.1 before 16.5.1, and from 17.0.0 before 17.2.2, are vulnerable to privilege escalation. An authenticated backoffice user who already has access to the Users section can modify user group memberships to gain Administrator rights, which gives full control of the instance. Upgrade to 16.5.1 or 17.2.2. No workaround other than upgrading is listed for setups that must give Users-section access without granting Administrator membership.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 7.2 | High | 3.1 | CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0038, the 31st percentile, on 10 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 10 Mar 2026, 05:31 UTC Published by the maintainers as a GitHub repository advisory
- 31 Oct 2026, 15:22 UTC First seen by agentprime
- 31 Oct 2026, 15:22 UTC Confirmed by OSV