CVE-2026-50279: Craft CMS Authorship Spoofing Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qq2c-2q8j-jh27",
  "modified" : "2026-07-02T18:45:28Z",
  "published" : "2026-07-02T18:45:28Z",
  "aliases" : [ "CVE-2026-50279" ],
  "summary" : "Craft CMS: Authorship spoofing in `entries/save-entry` via pre-check/post-mutation authorization gap",
  "details" : "### Summary\n\n`EntriesController::actionSaveEntry()` performs entry-edit permission checks before request-controlled author changes are applied to the model. The subsequent author mutation path accepts attacker-supplied `authors` / `author` parameters and allows the change when the current user is one of the old authors. Because the controller does not re-run authorization after mutating the author list, a low-privileged user can reassign an entry’s authorship to another user without holding the dedicated peer-author-change permission.\n\n### Details\nThe control flow begins in [EntriesController.php](/D:/files/projects/cms-5.9.19/cms-5.9.19/src/controllers/EntriesController.php):249. `actionSaveEntry()` loads the entry and enforces edit permissions before calling `_populateEntryModel()`:\n\n```php\npublic function actionSaveEntry(bool $duplicate = false): ?Response\n{\n    ...\n    $entry = $this->_editableEntry($this->request->getBodyParam('entryId'), $siteId);\n    ...\n    $this->enforceEditEntryPermissions($entry, $duplicate);\n    ...\n    $this->_populateEntryModel($entry);\n    ...\n    $success = Craft::$app->getElements()->saveElement($entry);\n}\n```\n\nThe attacker-controlled source is in [EntriesController.php](/D:/files/projects/cms-5.9.19/cms-5.9.19/src/controllers/EntriesController.php):588:\n\n```php\n$entry->setAttributesFromRequest(array_filter([\n    'authorIds' => $this->request->getBodyParam('authors') ??\n        $this->request->getBodyParam('author') ??\n        $entry->getAuthorId() ??\n        static::currentUser()->id,\n]));\n```\n\n`Entry::setAttributesFromRequest()` in [Entry.php](/D:/files/projects/cms-5.9.19/cms-5.9.19/src/elements/Entry.php):1124 extracts the new author IDs and applies them if `canChangeAuthor()` returns true:\n\n```php\nif (\n    ($authorIds !== null || $authorId !== null) &&\n    $this->canChangeAuthor()\n) {\n    $this->_oldAuthorIds = $oldAuthorIds;\n    $this->setAuthorIds($authorIds);\n}\n```\n\n`canChangeAuthor()` at [Entry.php](/D:/files/projects/cms-5.9.19/cms-5.9.19/src/elements/Entry.php):2789 allows the author change when the current user can view peer entries and is already one of the existing authors:\n\n```php\nreturn (\n    empty($authorIds) ||\n    in_array($user->id, $authorIds) ||\n    $user->can(\"changeAuthorForPeerEntries:$section->uid\")\n);\n```\n\nAfter the author list is mutated, the controller does not re-check authorization. \n\nThis closes the exploit chain:\n\n1. External source: authenticated request to `entries/save-entry` with attacker-controlled `authors[]`.\n2. Trust boundary failure: authorization is checked on the pre-mutation entry state, not on the post-mutation author assignment.\n3. Privileged sink: the author relationship is rewritten in persistent storage.\n\nPreconditions derived from the source:\n\n1. The attacker is authenticated and can edit entry `345`.\n2. The attacker is among the existing authors of entry `345`, or otherwise satisfies `canChangeAuthor()` through the old author set.\n3. The attacker has `viewPeerEntries` for the section.\n4. User ID `1` exists and can be assigned as an author in that section.\n\nResult:\n\n1. `enforceEditEntryPermissions()` succeeds on the original entry state.\n2. `_populateEntryModel()` reads `authors[]=1` from the request body.\n3. `setAttributesFromRequest()` updates `authorIds` because `canChangeAuthor()` is evaluated against the old authorship state.\n4. `saveElement()` persists the change and `_saveAuthors()` rewrites the entry-author relation.\n5. Entry `345` now appears authored by user `1`.\n\n### Impact\n\nThis allows low-privileged users to falsify content ownership and alter the authorship of entries without having the dedicated author-management permission. The impact includes corrupted audit trails, misleading notifications, broken approval workflows, and unauthorized reassignment of content responsibility.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "craftcms/cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0-RC1"
      }, {
        "fixed" : "5.9.21"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/security/advisories/GHSA-qq2c-2q8j-jh27"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-50279"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/craftcms/cms/commit/9cc493be8b414d7116c7f2bc2a6d0926e73f1248"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/craftcms/cms"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-285" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-02T18:45:28Z",
    "nvd_published_at" : "2026-07-02T00:16:44Z"
  }
}