Summary
Craft CMS has a Missing Authorization Check on User Group Removal via save-permissions Action
The actionSavePermissions() endpoint allows a user with only viewUsers permission to remove arbitrary users from all user groups. While _saveUserGroups() enforces per-group authorization for additions, it performs no equivalent authorization check for removals, so submitting an empty groups value removes all existing group memberships.
Affected Versions
- Craft CMS 5.6.0 through 5.9.14 (latest release at time of report)
- Regression introduced in 5.6.0 when the
viewUserspermission was added - Prior to 5.6.0,
editedUser()requirededitUsers, which implicitly protected this endpoint - Requires Pro edition or higher (the vulnerable code path is gated by
CmsEdition::Pro)
Vulnerability Details
Root Cause
This is a regression introduced in Craft CMS 5.6.0 when the viewUsers permission was added. Before that change, editedUser() required editUsers permission for accessing other users’ data, which implicitly protected actionSavePermissions(). After the change, actionSavePermissions() became reachable for users with read-only access to other users, but the underlying group-saving logic still lacked authorization for group removals.
The vulnerability has two components:
actionSavePermissions()reachable with read-only access: The action only requires a control panel request and delegates toeditedUser(), which now only checksviewUsers, a permission explicitly documented as "read-only access to user elements."Asymmetric authorization in
_saveUserGroups(): The method checksassignUserGrouppermission only when adding a user to a new group. When thegroupsparameter is an empty string (resulting in an empty array), the loop is skipped entirely, no authorization checks are run, and all group memberships are removed.
Prerequisites
- Attacker has a control panel account with
accessCpandviewUserspermissions only - Target user belongs to one or more user groups that grant additional permissions
- Pro edition or higher
Attack Steps
- Attacker authenticates to the Control Panel
- Attacker sends a POST request to
actions/users/save-permissionswith:userId= target user's IDgroups= `` (empty string)
- All group memberships for the target user are removed
- All permissions inherited from those groups are immediately revoked
Impact
- Privilege revocation: An attacker can strip group-based permissions from arbitrary users, including accounts whose effective access derives from group membership
- Denial of access: Users lose access to sections, volumes, and features that were granted through group membership
- Bypass of elevated session requirement: Group removal does not trigger
requireElevatedSession()(which is only triggered when new groups are added)
The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-41128? CVE-2026-41128 is a medium-severity missing authorization vulnerability in craftcms/cms (composer), affecting versions >= 5.6.0, < 5.9.15. It is fixed in 5.9.15. The application does not perform an authorization check before performing a sensitive operation.
- Which versions of craftcms/cms are affected by CVE-2026-41128? craftcms/cms (composer) versions >= 5.6.0, < 5.9.15 is affected.
- Is there a fix for CVE-2026-41128? Yes. CVE-2026-41128 is fixed in 5.9.15. Upgrade to this version or later.
- Is CVE-2026-41128 exploitable, and should I be worried? Whether CVE-2026-41128 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-41128 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-41128? Upgrade
craftcms/cmsto 5.9.15 or later.