CVE-2026-31834: Umbraco.Cms Umbraco Affected By Vertical Privilege Vulnerability

HIGH
Advisory Identifier: GHSA-rhcg-3h8r-v6vp
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CVSS 7.2
CWE-269
Published
Advisory Summary

CVE-2026-31834 is a HIGH (CVSS 7.2) umbraco affected by vertical privilege vulnerability (CWE-269: Improper Privilege Management) affecting Umbraco.Cms libraries in the NuGet ecosystem. The issue involves umbraco affected by vertical privilege escalation via missing authorization checks. Remediation is available by upgrading affected packages to version 16.5.1, 17.2.2.

CVE-2026-31834 at a Glance

CVE Identifier CVE-2026-31834
GHSA Identifier GHSA-rhcg-3h8r-v6vp
Severity HIGH
CVSS v3.1 Base Score 7.2
CWE Classification CWE-269: Improper Privilege Management
Affected Product Umbraco.Cms
Package Ecosystem NuGet
Published Date
Last Updated

Security Impact

CVSS: 7.2

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required High (PR:H)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-31834

To remediate this vulnerability, upgrade all affected Umbraco.Cms dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Umbraco.Cms fixed: 16.5.1 
Upgrade Umbraco.Cms to 16.5.1
Umbraco.Cms fixed: 17.2.2 
Upgrade Umbraco.Cms to 17.2.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for Umbraco.Cms

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-31834, inspect your project dependencies for Umbraco.Cms:

inspect dependencies for Umbraco.Cms

Analyze the terminal output to locate any version of Umbraco.Cms in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 16.5.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-269: Improper Privilege Management, where the product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. In Umbraco.Cms, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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.

CVE-2026-31834 Affected Umbraco.Cms Versions

2 component(s)
Fixed Versions:
16.5.117.2.2
Product / Package Ecosystem Affected Versions Fixed Version
Umbraco.Cms
nuget/Umbraco.Cms
NuGet
≥ 15.3.1
< 16.5.1
16.5.1
Umbraco.Cms
nuget/Umbraco.Cms
NuGet
≥ 17.0.0
< 17.2.2
17.2.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rhcg-3h8r-v6vp
NVD — CVE-2026-31834 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-31834
Umbraco.Cms Source Repository REPOSITORY
https://github.com/umbraco/Umbraco-CMS

Frequently Asked Questions

What is CVE-2026-31834?
CVE-2026-31834 is a security vulnerability in Umbraco.Cms involving Umbraco Affected by Vertical Privilege Escalation via Missing Authorization Checks under CWE-269: Improper Privilege Management.
Which Umbraco.Cms versions are affected?
Affected versions include releases prior to 16.5.1, 17.2.2 across affected packages: Umbraco.Cms.
What version fixes CVE-2026-31834?
Upgrading to 16.5.1, 17.2.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is Umbraco.Cms affected?
Yes, Umbraco.Cms is affected in releases prior to 16.5.1, 17.2.2. Upgrade your dependency to 16.5.1, 17.2.2 or later.
What is the CVSS score of CVE-2026-31834?
CVE-2026-31834 has a CVSS v3.1 base score of 7.2 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2026-31834?
CVE-2026-31834 is classified under CWE-269: Improper Privilege Management (The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.).
How can I check NuGet dependencies for CVE-2026-31834?
Run the dependency tree command: 'inspect dependencies for Umbraco.Cms'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-rhcg-3h8r-v6vp",
  "modified" : "2026-03-11T14:54:05Z",
  "published" : "2026-03-11T14:54:05Z",
  "aliases" : [ "CVE-2026-31834" ],
  "summary" : "Umbraco Affected by Vertical Privilege Escalation via Missing Authorization Checks",
  "details" : "### Description\nA 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.\n\nThe affected functionality does not properly validate whether a user has sufficient privileges to assign highly privileged roles.\n\n### Impact\nAn authenticated backoffice user may be able to escalate their privileges to Administrator level.\n\nSuccessful exploitation results in full administrative control of the affected Umbraco CMS instance, including unrestricted access to content, user management, and configuration settings.\n\nThe 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\".\n\n### Patches\nThe issue is patched in 16.5.1 and 17.2.2.\n\n### Workarounds\nThere 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Umbraco.Cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "15.3.1"
      }, {
        "fixed" : "16.5.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Umbraco.Cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "17.0.0"
      }, {
        "fixed" : "17.2.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rhcg-3h8r-v6vp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-31834"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/umbraco/Umbraco-CMS"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-269" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-11T14:54:05Z",
    "nvd_published_at" : "2026-03-10T22:16:21Z"
  }
}