CVE-2026-31834 | Umbraco Affected by Vertical Privilege Escalation via Missing Authorization Checks

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.

Published: 2026-03-10 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-31834 is rated Low Risk (34.9/100): CVSS High severity, with low exploitation likelihood (EPSS 0.26%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-31834

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.05% 0.26% +0.21%
2 2026-03-19 0.04% 0.05% +0.01%
3 2026-03-11 — 0.04% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-31834

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.2 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:H)
They need powerful rights—admin, root, or similar—before this pays off.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.2 5.9 [email protected]

Weakness enumeration for CVE-2026-31834

GitHub Security Advisory for CVE-2026-31834

GHSA-rhcg-3h8r-v6vp · Severity: high · Ecosystem: nuget — Umbraco Affected by Vertical Privilege Escalation via Missing Authorization Checks

Affected software / configurations for CVE-2026-31834

Vendor Product Version Raw CPE
umbraco umbraco_cms >= 15.3.1, < 16.5.1 cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*
umbraco umbraco_cms >= 17.0.0, < 17.2.2 cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*

References for CVE-2026-31834

cvelogic Threat Intelligence