CVE-2026-42609: Getgrav/grav Grav Vulnerable To Administrative Account Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-rr73-568v-28f8",
  "modified" : "2026-05-13T13:52:30Z",
  "published" : "2026-05-05T21:29:53Z",
  "aliases" : [ "CVE-2026-42609" ],
  "summary" : "Grav Vulnerable to Administrative Account Disruption and Privilege De-escalation via User Overwrite Logic",
  "details" : "### Summary\nA business logic vulnerability in the Grav Admin Panel allows a low-privileged user (with only user creation permissions) to overwrite existing accounts, including the primary administrator. By creating a new user with a username that already exists, the system updates the existing account's metadata and permissions instead of rejecting the request. This leads to a Denial of Service (DoS) on administrative functions and Privilege De-escalation of the root account.\n\n### Details\nThe vulnerability stems from an insecure \"Create or Update\" logic within the user management module. When the admin-addon handles a user creation request, it does not strictly validate whether the username is already taken by a higher-privileged account. Instead of returning a \"409 Conflict\" or a validation error, the application logic proceeds to overwrite the existing user configuration file (e.g., user/accounts/root0.yaml) with the new, lower-privileged data provided by the attacker.\nBecause the attacker cannot assign higher permissions to themselves (due to existing fixes), the result is that the targeted account (the original Admin/Root) has its access levels wiped or replaced by the attacker's input, effectively locking the real administrator out of the system.\n\n### PoC\n1. Log in as a Super User (e.g., root0) and create a low-privileged user (e.g., adminuser).\n2. Assign adminuser the following specific permissions:\nadmin.login\nadmin.users.list\nadmin.users.read\nadmin.users.create\n3. Log out and log back in as adminuser.\n4. Navigate to User Accounts -> Add.\n5. Fill in the form with the following details:\nUsername: root0 (The exact username of the Super User)\nEmail: `anything@grav.f`\nFullname: Fake Root0\n7. Click Save.\n8. Observe that the account is successfully \"created\".\n9. The original administrative permissions are gone, and the account is now restricted.\n\n#### PoC video\nhttps://github.com/user-attachments/assets/047cb44e-0279-402b-b4fb-12bf5d427a5e\n\n### Impact\nThis is a Privilege De-escalation and Account Disruption vulnerability.\nWho is impacted: Any Grav installation where a non-admin user is granted permission to create other users.\nConsequence: An attacker can effectively disable all administrative accounts on the platform, leading to a complete loss of management control over the CMS.\n\n\n---\n\n## Maintainer note — fix applied (2026-04-24)\n\nFixed in Grav core on the `2.0` branch: commit [`d904efc33`](https://github.com/getgrav/grav/commit/d904efc33) — will ship in **2.0.0-beta.2**.\n\n**What changed:** `UserObject::save` already had a uniqueness guard (commit [`19c2f8da7`](https://github.com/getgrav/grav/commit/19c2f8da7), November 2025) that blocks the PoC. This release tightens that guard:\n\n1. `strpos($key, '@@')` → `str_contains($key, '@@')`. The previous form was falsy when the transient-key marker was at position 0 (e.g. `@@hash`), silently bypassing the check. `str_contains` returns a proper boolean.\n2. The `instanceof FileStorage` gate was dropped so the uniqueness check runs for any `FlexStorageInterface` backend — not just the default file-per-user YAML one.\n\nA low-privileged user with `admin.users.create` can no longer disrupt a super-admin account by submitting that admin's username through the \"add user\" form.\n\n**Files:**\n- [`system/src/Grav/Common/Flex/Types/Users/UserObject.php`](https://github.com/getgrav/grav/blob/2.0/system/src/Grav/Common/Flex/Types/Users/UserObject.php).\n- [`tests/unit/Grav/Common/Security/UserOverwriteSecurityTest.php`](https://github.com/getgrav/grav/blob/2.0/tests/unit/Grav/Common/Security/UserOverwriteSecurityTest.php) — 3 tests pinning the PoC, the `@@`-prefix edge case, and pass-through for free usernames.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "getgrav/grav"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.0.0-beta.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/security/advisories/GHSA-rr73-568v-28f8"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42609"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/commit/5a12f9be8314682c8713e569e330f11805d0a663"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/commit/c66dfeb5ff679a1667678c6335eb9ff3255dfc47"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/commit/d904efc33e03ebb597afde8d3368b28cf0423632"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/getgrav/grav"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-269", "CWE-285", "CWE-639", "CWE-837" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T21:29:53Z",
    "nvd_published_at" : "2026-05-11T16:17:33Z"
  }
}