Security fixes: CSV injection, policy body output, invite hashing, slot datetimes

Four fixes from a security review pass:

- Neutralise CSV formula injection in the payments export: fields with a
  leading =, +, -, @, tab, or CR (e.g. a hostile student display name) are
  apostrophe-prefixed in PaymentReport::csvLine() so they open as text in
  Excel/Google Sheets. Fixes #39.
- Sanitise policy bodies with wp_kses_post at output in
  PolicyEndpoint::index() (the booking JS renders that HTML raw), so a
  future write path that forgets kses can never become stored XSS.
  Fixes #40.
- Store invite tokens hashed (SHA-256) at rest: a database leak can no
  longer redeem pending invites. The registration link is shown once, at
  creation; the pending list shows email/invited date; lookups hash the
  submitted token. Existing plaintext pending invites must be re-issued.
  Fixes #41.
- Validate availability slot datetimes on both creation paths (REST and
  admin form) via AvailabilitySlot::normalizeDateTime(): canonical and
  datetime-local forms normalise to Y-m-d H:i:s, garbage and end <= start
  are rejected (REST 400) instead of reaching the DATETIME column or
  throwing inside the weekly-series date arithmetic. Fixes #42.

composer test (204 tests, 594 assertions), PHPStan L6, and PHPCS all green.

Co-Authored-By: Claude Fable 5 <[email protected]>

src/Auth/Invite.php

@@ -22,6 +22,16 @@ class Invite {
 	 */
 	public const EXPIRY_DAYS = 14;
 
+	/**
+	 * Hash a raw invitation token for storage and lookup. Only the hash is
+	 * persisted, so a database leak (backup, SQL injection elsewhere) cannot be
+	 * used to redeem pending invites; the raw token exists only in the emailed
+	 * link and is shown to the admin once, at creation.
+	 */
+	public static function hashToken( string $rawToken ): string {
+		return hash( 'sha256', $rawToken );
+	}
+
 	public function __construct(
 		public readonly string $email,
 		public readonly string $token,

src/Auth/RegistrationController.php

@@ -17,8 +17,9 @@ class RegistrationController {
 			wp_die( esc_html__( 'You do not have permission to manage invites.', 'unsupervised-schedular' ) );
 		}
 
+		$newInviteUrl = '';
 		if ( isset( $_POST['usc_action'] ) && check_admin_referer( 'usc_invite_action' ) ) {
-			$this->handleFormAction();
+			$newInviteUrl = $this->handleFormAction();
 		}
 
 		$pendingInvites      = $this->invites->findPending();
@@ -28,7 +29,12 @@ class RegistrationController {
 		include USC_PLUGIN_DIR . 'templates/admin/invites.php';
 	}
 
-	private function handleFormAction(): void {
+	/**
+	 * Handle a posted admin action. Returns the registration link for a freshly
+	 * created invite — the only time it can be shown, since just the token's hash
+	 * is stored — or an empty string for every other action.
+	 */
+	private function handleFormAction(): string {
 		// Nonce is verified by the caller (renderPage) before this method runs.
 		// phpcs:disable WordPress.Security.NonceVerification.Missing
 		$action = sanitize_key( wp_unslash( $_POST['usc_action'] ?? '' ) );
@@ -45,13 +51,17 @@ class RegistrationController {
 				&& false === email_exists( $email )
 				&& null === $this->invites->findPendingByEmail( $email )
 			) {
+				$rawToken = wp_generate_password( 32, false );
+
 				$this->invites->insert(
 					new Invite(
 						email:     $email,
-						token:     wp_generate_password( 32, false ),
+						token:     Invite::hashToken( $rawToken ),
 						invitedBy: get_current_user_id(),
 					)
 				);
+
+				return $this->registrationLink( $rawToken );
 			}
 		}
 
@@ -62,5 +72,17 @@ class RegistrationController {
 			}
 		}
 		// phpcs:enable WordPress.Security.NonceVerification.Missing
+
+		return '';
+	}
+
+	/**
+	 * Build the registration URL for a raw invite token.
+	 */
+	private function registrationLink( string $rawToken ): string {
+		$pageId   = (int) get_option( self::OPTION_PAGE, 0 );
+		$linkBase = $pageId > 0 ? (string) get_permalink( $pageId ) : '';
+
+		return add_query_arg( 'us_invite', rawurlencode( $rawToken ), '' !== $linkBase ? $linkBase : home_url( '/' ) );
 	}
 }

src/Auth/RegistrationPage.php

@@ -29,8 +29,9 @@ class RegistrationPage {
 		}
 
 		// phpcs:ignore WordPress.Security.NonceVerification.Recommended -- token identifies the invite; the form submit is nonce-checked below.
-		$token  = sanitize_text_field( wp_unslash( $_REQUEST['us_invite'] ?? '' ) );
-		$invite = '' !== $token ? $this->invites->findByToken( $token ) : null;
+		$token = sanitize_text_field( wp_unslash( $_REQUEST['us_invite'] ?? '' ) );
+		// Only the token's hash is stored, so hash the submitted token for lookup.
+		$invite = '' !== $token ? $this->invites->findByToken( Invite::hashToken( $token ) ) : null;
 
 		$error   = '';
 		$success = false;

src/Availability/AvailabilityController.php

@@ -54,10 +54,10 @@ class AvailabilityController {
 
 	private function addSlot( int $instructorId ): void {
 		// phpcs:disable WordPress.Security.NonceVerification.Missing
-		$startDt = sanitize_text_field( wp_unslash( $_POST['start_dt'] ?? '' ) );
-		$endDt   = sanitize_text_field( wp_unslash( $_POST['end_dt'] ?? '' ) );
+		$startDt = AvailabilitySlot::normalizeDateTime( sanitize_text_field( wp_unslash( $_POST['start_dt'] ?? '' ) ) );
+		$endDt   = AvailabilitySlot::normalizeDateTime( sanitize_text_field( wp_unslash( $_POST['end_dt'] ?? '' ) ) );
 
-		if ( '' === $startDt || '' === $endDt ) {
+		if ( null === $startDt || null === $endDt || $endDt <= $startDt ) {
 			return;
 		}
 

src/Availability/AvailabilityEndpoint.php

@@ -120,10 +120,17 @@ class AvailabilityEndpoint {
 			}
 		}
 
+		$startDt = AvailabilitySlot::normalizeDateTime( (string) $request->get_param( 'start_dt' ) );
+		$endDt   = AvailabilitySlot::normalizeDateTime( (string) $request->get_param( 'end_dt' ) );
+
+		if ( null === $startDt || null === $endDt || $endDt <= $startDt ) {
+			return new \WP_Error( 'invalid_datetime', __( 'Provide a valid start and end, with the end after the start.', 'unsupervised-schedular' ), [ 'status' => 400 ] );
+		}
+
 		$slot = new AvailabilitySlot(
 			instructorId:    $instructorId,
-			startDt:         (string) $request->get_param( 'start_dt' ),
-			endDt:           (string) $request->get_param( 'end_dt' ),
+			startDt:         $startDt,
+			endDt:           $endDt,
 			durationMinutes: $duration > 0 ? $duration : 60,
 			offeringId:      $offeringId > 0 ? $offeringId : null,
 		);

src/Availability/AvailabilitySlot.php

@@ -16,6 +16,25 @@ class AvailabilitySlot {
 		public readonly ?int $id = null,
 	) {}
 
+	/**
+	 * Normalise a submitted slot datetime to canonical `Y-m-d H:i:s`, or null when
+	 * it is not a real datetime. Accepts the HTML `datetime-local` form
+	 * (`Y-m-d\TH:i`, optionally with seconds) and the canonical form (optionally
+	 * without seconds). Anything else — including strings PHP would "helpfully"
+	 * coerce — is rejected so garbage never reaches the DATETIME column or throws
+	 * inside the weekly-series date arithmetic.
+	 */
+	public static function normalizeDateTime( string $value ): ?string {
+		foreach ( [ 'Y-m-d H:i:s', 'Y-m-d H:i', 'Y-m-d\TH:i:s', 'Y-m-d\TH:i' ] as $format ) {
+			$dt = \DateTimeImmutable::createFromFormat( '!' . $format, $value );
+			if ( false !== $dt && $dt->format( $format ) === $value ) {
+				return $dt->format( 'Y-m-d H:i:s' );
+			}
+		}
+
+		return null;
+	}
+
 	public static function fromRow( object $row ): self {
 		return new self(
 			instructorId:    (int) $row->instructor_id,

src/Payment/PaymentReport.php

@@ -90,13 +90,22 @@ class PaymentReport {
 	}
 
 	/**
-	 * Format one CSV record, quoting fields and escaping embedded quotes.
+	 * Format one CSV record, quoting fields and escaping embedded quotes. Fields
+	 * that a spreadsheet would interpret as a formula (leading =, +, -, @, tab, or
+	 * CR — e.g. a hostile student display name) are prefixed with an apostrophe so
+	 * they open as text, never as executable formulas.
 	 *
 	 * @param list<string> $fields
 	 */
 	private function csvLine( array $fields ): string {
 		$escaped = array_map(
-			static fn( string $field ): string => '"' . str_replace( '"', '""', $field ) . '"',
+			static function ( string $field ): string {
+				if ( 1 === preg_match( '/^[=+\-@\t\r]/', $field ) ) {
+					$field = "'" . $field;
+				}
+
+				return '"' . str_replace( '"', '""', $field ) . '"';
+			},
 			$fields
 		);
 

src/Policy/PolicyEndpoint.php

@@ -97,7 +97,10 @@ class PolicyEndpoint {
 				'slug'              => $policy->slug,
 				'policy_version_id' => $version->id,
 				'version_number'    => $version->versionNumber,
-				'body'              => $version->body,
+				// Bodies are kses'd on every write path, but the booking JS renders
+				// this HTML raw — sanitise at output too so a missed write path can
+				// never become stored XSS.
+				'body'              => wp_kses_post( (string) $version->body ),
 			];
 		}