CVE-2026-55824

Ein entfernter, authentisierter Angreifer kann mehrere Schwachstellen in Contao ausnutzen, um Informationen offenzulegen.

### Summary Contao's crawler tries to prevent confidential HTTP client options from being sent to external domains by creating a scoped client: full options for root page origins, cleaned options for everything else. The cleaner removes `Cookie` and `Authorization` headers, but it removes the non-Symfony option names `basic_auth` and `bearer_auth` instead of Symfony HttpClient's real `auth_basic` and `auth_bearer` options. When `contao.crawl.default_http_client_options` contains Basic or Bearer authentication for a protected staging/production site, those credentials remain in the "clean" client used for external links or configured additional URIs. An attacker who can get an external URL crawled, for example through a link on a crawled page while the broken-link checker is enabled, can receive the crawler credentials. ## Technical Detail ### Root Cause ```php // core-bundle/src/Crawl/Escargot/Factory.php:175-209 @ e550b92a01ef625bd546e6c3956dd200af05ebf0 private function createHttpClient(array $options = []): HttpClientInterface { $options = array_merge_recursive( [ 'headers' => [ 'accept' => 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'user-agent' => self::USER_AGENT, ], 'max_duration' => 10, ], array_merge_recursive($this->getDefaultHttpClientOptions(), $options), ); $cleanOptions = $this->cleanOptionsFromConfidentialData($options); if ($options === $cleanOptions) { return ($this->httpClientFactory)($options); } $scopedOptionsByRegex = []; foreach ($this->getRootPageUriCollection()->all() as $rootPageUri) { $scopedOptionsByRegex[preg_quote($this->getOriginFromUri($rootPageUri))] = $options; } return new ScopingHttpClient(($this->httpClientFactory)($cleanOptions), $scopedOptionsByRegex); } ``` ```php // core-bundle/src/Crawl/Escargot/Factory.php:226-247 @ e550b92a01ef625bd546e6c3956dd200af05ebf0 foreach ($options as $k => $v) { if ('headers' === $k) { foreach ($v as $header => $value) { if (\in_array(strtolower($header), ['authorization', 'cookie'], true)) { continue; } $cleanOptions['headers'][$header] = $value; } continue; } if ('basic_auth' === $k || 'bearer_auth' === $k) { continue; } $cleanOptions[$k] = $v; } ``` Symfony HttpClient authentication options are `auth_basic` and `auth_bearer`; Contao's own manual documents `auth_basic` for crawler Basic Authentication. Because the cleaner only strips `basic_auth` and `bearer_auth`, the "clean" default client for non-root-page hosts still carries the real auth options. The existing factory test intends to assert that `Authorization` is not sent to `www.foreign-domain.com`, but its mock client factory ignores the `$defaultOptions` argument, so it does not catch auth options that survive into `HttpClient::create($cleanOptions)`. ## Suggested Mitigation Strip the actual Symfony HttpClient authentication option keys from the clean client. Include NTLM as a defensive extension because Symfony documents it as another auth option. ```diff - if ('basic_auth' === $k || 'bearer_auth' === $k) { + if (\in_array($k, ['auth_basic', 'auth_bearer', 'auth_ntlm', 'basic_auth', 'bearer_auth'], true)) { continue; } ``` Also update the factory test so the mock factory records or preserves `$defaultOptions`; otherwise the test does not verify what `HttpClient::create($cleanOptions)` receives in production. ## Impact - **Direct primitive**: disclosure of crawler Basic/Bearer credentials to an external host reached by the crawler. - **Chain potential**: if those credentials protect a staging or pre-publication environment, an attacker can use them to access that environment. The impact depends on what the leaked credential unlocks. - **Realistic exploitation**: a content editor adds a link to `https://attacker.example/probe` on a page that the crawler visits. When an administrator or scheduled maintenance run starts the broken-link checker with crawler Basic/Bearer authentication configured, the request to the attacker URL includes the generated `Authorization` header.