GHSA-4f5f-j737-pm58

### Summary The `rex_list` component reads the SQL sort column directly from the `sort` GET parameter without validating it against the set of columns declared sortable via `setColumnSortable()`. Although the value is wrapped in backticks via `escapeIdentifier()` (preventing classical SQL injection), this still allows any authenticated backend user to ORDER BY any column in the query's FROM tables, including unselected sensitive columns such as `password` from the `rex_user` table, and perform error-based column enumeration.

### Details **File:** `redaxo/src/core/lib/list.php:976-982` — `getSortColumn()` returns the raw request parameter without whitelist check: ```php public function getSortColumn($default = null) { if (rex_request('list', 'string') == $this->getName()) { return rex_request('sort', 'string', $default); // NO validation against sortable columns } return $default; } ```

**File:** `redaxo/src/core/lib/list.php:899-911` — `prepareQuery()` uses it directly in the ORDER BY clause: ```php protected function prepareQuery($query, array $defaultSort = []) { $sortColumn = $this->getSortColumn(); if ('' != $sortColumn) { $sql = rex_sql::factory($this->db); $sortColumn = $sql->escapeIdentifier($sortColumn); // backtick-wraps, but no whitelist if ($defaultSort || false === stripos($query, ' ORDER BY ')) { $query .= ' ORDER BY ' . $sortColumn . ' ' . $sortType; } } ```

The users list queries `rex_user` which contains `password`, `previous_passwords`, `password_change_required` — not in the SELECT. Specifying a non-existent column name produces a MySQL `Unknown column` exception whose message is propagated to the user, confirming or denying column existence.

### PoC **Column enumeration (error-based):** ``` GET /redaxo/index.php?page=users&list=<list_name>&sort=nonexistent_col&sorttype=asc ``` Response will contain: `Unknown column 'nonexistent_col' in 'order clause'`

**Sort by password hash (data ordering leak):** ``` GET /redaxo/index.php?page=users&list=<list_name>&sort=password&sorttype=asc ``` Users are silently reordered by their Argon2 password hash.

### Impact Authenticated backend users (non-admin) can enumerate database column names of internal tables via error messages and manipulate query ordering to include sensitive unselected columns. While this does not allow arbitrary SQL execution due to backtick escaping, it constitutes an information disclosure vulnerability enabling targeted further attacks.

### Fix Validate the `sort` request parameter against the whitelist of columns registered with `setColumnSortable()` before use in the query: ```php public function getSortColumn($default = null) { if (rex_request('list', 'string') == $this->getName()) { $requested = rex_request('sort', 'string', $default); if ($requested !== null && $this->hasColumnOption($requested, REX_LIST_OPT_SORT)) { return $requested; } } return $default; } ```