Umbraco Cms
CVE-2026-31834
HIGH
GHSA-rhcg-3h8r-v6vp
Severity by source
AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
3DescriptionGitHub Advisory
Umbraco is an ASP.NET CMS. From 15.3.1 to before 16.5.1 and 17.2.2, 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. This vulnerability is fixed in 16.5.1 and 17.2.2.
AnalysisAI
Privilege escalation in Umbraco CMS versions 15.3.1 through 16.5.0 and 17.x before 17.2.2 allows authenticated backoffice users with user management permissions to assign themselves elevated privileges by bypassing authorization checks on role assignments. An attacker with these permissions could gain administrative access to the CMS without proper privilege validation. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Authenticated backoffice user with permission to manage users in Umbraco CMS versions 15.3.1 through 16.5.0 or 17.0.0 through 17.2.1. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | CVSS 7.2 (HIGH). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker (requires authentication) could exploit this vulnerability to compromise the affected system. |
| Remediation | Fixed in version 16.5.1. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Inventory all Umbraco installations and verify version numbers; audit recent user group membership changes in backoffice logs for unauthorized privilege escalation attempts. …
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External POC / Exploit Code
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