JezK

Edit File: unauth-file-upload.php

<?php
/**
 * Unauthenticated File Upload Helper Functions.
 *
 * @package automattic/jetpack
 */

namespace Automattic\Jetpack\UnauthFileUpload;

if ( ! defined( 'ABSPATH' ) ) {
	exit( 0 );
}

add_action( 'wp_ajax_jetpack_unauth_file_download', __NAMESPACE__ . '\handle_file_download' );
add_filter( 'jetpack_unauth_file_upload_get_file', __NAMESPACE__ . '\get_file_content', 10, 2 );
add_filter( 'jetpack_unauth_file_download_url', __NAMESPACE__ . '\filter_get_download_url', 10, 2 );

/**
 * The lifetime of a download link, in seconds.
 *
 * Kept generous enough that an editor returning to the responses dashboard days later still
 * has a working link, short enough to limit the exposure of a leaked URL.
 */
const DOWNLOAD_LINK_LIFETIME = 7 * DAY_IN_SECONDS;

/**
 * The token scheme version carried in download links.
 *
 * Travels in the URL as `token_version` and is bound into the signature, so the signing scheme
 * can be changed in the future (bump this and branch on the value in authorize_file_download())
 * without older links being mistaken for the new format.
 */
const DOWNLOAD_TOKEN_VERSION = 'v1';

/**
 * Get the secret used to sign download links.
 *
 * Defaults to the Jetpack blog token, which this feature already depends on (the file content
 * is fetched from WP.com as the blog). There is nothing extra to store, and reconnecting
 * Jetpack rotates the token and so invalidates any outstanding links. Only the secret portion
 * of the token (after the publicly-visible key prefix) is used, matching the rest of the
 * connection stack.
 *
 * @since 16.0
 *
 * @return string The signing key, or an empty string if no secret is available.
 */
function get_download_signing_key() {
	$blog_token = ( new \Automattic\Jetpack\Connection\Tokens() )->get_access_token();
	$secret     = '';

if ( $blog_token && ! is_wp_error( $blog_token ) && ! empty( $blog_token->secret ) ) {
		// Blog tokens are stored as "key.secret"; sign with the secret part only, matching the
		// rest of the connection stack. Require exactly two non-empty parts so a malformed token
		// fails closed rather than signing links the fetch path could never honor.
		$parts = explode( '.', (string) $blog_token->secret, 2 );
		if ( count( $parts ) === 2 && '' !== $parts[0] && '' !== $parts[1] ) {
			$secret = $parts[1];
		}
	}

/**
	 * Filters the secret used to sign Forms unauthenticated file-download links.
	 *
	 * Defaults to the Jetpack blog token secret. Environments without a usable blog token
	 * (e.g. WordPress.com Simple) can return their own stable, secret value here so that
	 * download links can still be signed and verified.
	 *
	 * @since 16.0
	 *
	 * @param string $secret The signing secret. Empty string if none is available.
	 */
	return (string) apply_filters( 'jetpack_unauth_file_download_signing_key', $secret );
}

/**
 * Generate a signed token authorizing the download of a given file.
 *
 * Unlike a WordPress nonce, the token is not tied to a specific user or session, so a link
 * generated by one logged-in editor works for any logged-in editor. The expiry timestamp is
 * part of the signed payload, so it cannot be tampered with to extend access.
 *
 * @since 16.0
 *
 * @param int    $file_id The file ID.
 * @param int    $expires Unix timestamp at which the link stops being valid.
 * @param string $version The token scheme version. Defaults to the current scheme.
 *
 * @return string The hex-encoded HMAC-SHA256 token, or an empty string if there is no signing key.
 */
function generate_download_token( $file_id, $expires, $version = DOWNLOAD_TOKEN_VERSION ) {
	$key = get_download_signing_key();

if ( '' === $key ) {
		return '';
	}

$payload = 'jetpack_unauth_file_download|' . $version . '|' . (int) $file_id . '|' . (int) $expires;
	return hash_hmac( 'sha256', $payload, $key );
}

/**
 * Verify a download token against the expected signature using a constant-time comparison.
 *
 * Expiry is checked separately by the caller so it can surface a distinct "expired" message.
 * Fails closed when no signing key is available (i.e. the site is not connected).
 *
 * @since 16.0
 *
 * @param int    $file_id The file ID.
 * @param int    $expires Unix timestamp the token was signed with.
 * @param string $token   The token supplied in the request.
 * @param string $version The token scheme version the token was signed with.
 *
 * @return bool True if the token matches.
 */
function verify_download_token( $file_id, $expires, $token, $version = DOWNLOAD_TOKEN_VERSION ) {
	$expected = generate_download_token( $file_id, $expires, $version );

return '' !== $expected
		&& is_string( $token ) && '' !== $token
		&& hash_equals( $expected, $token );
}

/**
 * Get the file download URL filter callback.
 *
 * @param string $url The file download URL.
 * @param int    $file_id The file ID.
 *
 * @return string The file download URL.
 */
function filter_get_download_url( $url, $file_id ) {
	$expires = time() + DOWNLOAD_LINK_LIFETIME;
	$token   = generate_download_token( $file_id, $expires );

if ( '' === $token ) {
		// No signing key (disconnected site, or WP.com Simple without the signing-key filter
		// wired). Return the passthrough so callers omit the link instead of handing out one
		// that can never work, and leave a breadcrumb for operators.
		error_log( 'Jetpack Forms: unable to sign file download link; no signing key available.' ); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
		return $url;
	}

return add_query_arg(
		array(
			'action'        => 'jetpack_unauth_file_download',
			'file_id'       => $file_id,
			'expires'       => $expires,
			'token_version' => DOWNLOAD_TOKEN_VERSION,
			'token'         => $token,
		),
		admin_url( 'admin-ajax.php' )
	);
}

/**
 * Reject a download request with the generic invalid-link error and a debug code, then exit.
 *
 * The message stays generic so it leaks nothing to the requester and stays actionable (a token
 * can be rejected simply because the blog token rotated on reconnect), while the appended code
 * identifies which check failed, so a user-reported screenshot is enough to locate the cause:
 *
 *   1 - Missing or unrecognized token_version.
 *   2 - Token signature did not verify.
 *   3 - Legacy nonce did not verify.
 *   4 - No token and no legacy nonce supplied.
 *
 * @since 16.0
 *
 * @param int $code Number identifying the failing check.
 *
 * @return void Terminates the request via wp_die().
 */
function invalid_download_link( $code ) {
	wp_die(
		esc_html(
			sprintf(
				/* translators: %d: error code used for debugging. */
				__( 'This download link is no longer valid. Reload the responses page to get a fresh link. (%d)', 'jetpack' ),
				(int) $code
			)
		),
		'',
		array( 'response' => 403 )
	);
}

/**
 * Authorize a download request and return the requested file ID.
 *
 * Holds the security-critical gate (capability check, then either the current signed-token
 * scheme or the legacy nonce fallback). Terminates the request via wp_die() on any failure and
 * only returns when the caller is allowed to download the file. Kept separate from the
 * file-serving logic in handle_file_download() so each branch is unit-testable without the
 * headers/exit of the serving path.
 *
 * @since 16.0
 *
 * @return int The validated file ID.
 */
function authorize_file_download() {
	if ( ! current_user_can( 'edit_pages' ) ) {
		wp_die( esc_html__( 'Sorry, you are not allowed to access this page.', 'jetpack' ), '', array( 'response' => 403 ) );
	}

$file_id = isset( $_GET['file_id'] ) ? absint( wp_unslash( $_GET['file_id'] ) ) : 0;

if ( ! $file_id ) {
		wp_die( esc_html__( 'Invalid file request.', 'jetpack' ), '', array( 'response' => 400 ) );
	}

$token = isset( $_GET['token'] ) ? sanitize_text_field( wp_unslash( $_GET['token'] ) ) : '';

if ( '' !== $token ) {
		// Current scheme: a site-signed, expiring token. Future schemes can branch on the version.
		$token_version = isset( $_GET['token_version'] ) ? sanitize_text_field( wp_unslash( $_GET['token_version'] ) ) : '';

if ( DOWNLOAD_TOKEN_VERSION !== $token_version ) {
			invalid_download_link( 1 );
		}

$expires = isset( $_GET['expires'] ) ? absint( wp_unslash( $_GET['expires'] ) ) : 0;

// A link is valid up to and including its expiry second; expired once time passes it.
		if ( ! $expires || $expires < time() ) {
			wp_die( esc_html__( 'This download link has expired. Reload the responses page to get a fresh link.', 'jetpack' ), '', array( 'response' => 410 ) );
		}

// $token_version was asserted equal to DOWNLOAD_TOKEN_VERSION above; pass the constant so
		// a future multi-version branch can't accidentally feed the request value back in.
		if ( ! verify_download_token( $file_id, $expires, $token, DOWNLOAD_TOKEN_VERSION ) ) {
			invalid_download_link( 2 );
		}
	} elseif ( isset( $_GET['_wpnonce'] ) ) {
		/*
		 * Backward compatibility for legacy per-file nonce links that may still be circulating
		 * in already-sent emails. WordPress nonces are only valid for ~24h, so these links
		 * expire on their own shortly after the signed-token scheme ships.
		 *
		 * @todo Remove this legacy nonce fallback in Jetpack 16.3 or later; links signed under
		 *       the old scheme self-expire within ~24h of the signed-token scheme shipping.
		 */
		if ( ! wp_verify_nonce( sanitize_text_field( wp_unslash( $_GET['_wpnonce'] ) ), 'jetpack_unauth_file_download_nonce_' . $file_id ) ) {
			invalid_download_link( 3 );
		}
	} else {
		invalid_download_link( 4 );
	}

return $file_id;
}

/**
 * Handle file download requests from the admin page.
 *
 * @return never This method never returns as it exits directly
 */
function handle_file_download() {
	$file_id = authorize_file_download();

/**
	 * Get the file content that we send to the user to download.
	 *
	 * @since 14.6
	 *
	 * @param array $file_content The file content.
	 * @param string $file_id The file ID.
	 *
	 * @return array|\WP_Error The file array, containing the content, name and type.
	 */
	$file = apply_filters( 'jetpack_unauth_file_upload_get_file', array(), $file_id );

if ( is_wp_error( $file ) || empty( $file ) || ! is_array( $file ) ) {
		wp_die( esc_html__( 'Error retrieving file content.', 'jetpack' ) );
	}

// Given $file can be manipulated by a filter, make sure everything is as it should be.
	$file['content'] = $file['content'] ?? '';
	$file['type']    = $file['type'] ?? 'application/octet-stream';
	$file['name']    = $file['name'] ?? '';

// phpcs:ignore WordPress.Security.NonceVerification.Recommended -- The request is already authorized in authorize_file_download() before reaching here.
	$is_preview = isset( $_GET['preview'] ) && 'true' === $_GET['preview'] && is_file_type_previewable( $file['type'] );

// Clean output buffer
	if ( ob_get_length() ) {
		ob_clean();
	}
	// Set headers for download
	header( 'Content-Type: ' . $file['type'] );

if ( ! $is_preview ) {
		// Forcing the file to be downloaded is important to prevent XSS attacks.
		header( 'Content-Disposition: attachment; filename="' . sanitize_file_name( $file['name'] ) . '"' );
	} else {
		// For preview mode, use inline disposition
		header( 'Content-Disposition: inline; filename="' . sanitize_file_name( $file['name'] ) . '"' );
	}
	header( 'Content-Length: ' . strlen( $file['content'] ) );
	header( 'Content-Transfer-Encoding: binary' );
	header( 'Cache-Control: no-cache, must-revalidate, max-age=0' );
	header( 'Pragma: no-cache' );
	header( 'Expires: 0' );

// Output file content and exit
	echo $file['content']; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Binary file data
	exit( 0 );
}

/**
 * Get the file content.
 *
 * @param array   $file_content The file content, name and type.
 * @param integer $file_id The file ID.
 * @return array|\WP_Error The file content, name and type
 */
function get_file_content( $file_content, $file_id ) {
	if ( ( new \Automattic\Jetpack\Status\Host() )->is_wpcom_simple() ) {
		return $file_content;
	}

$blog_id     = \Jetpack_Options::get_option( 'id' );
	$request_url = sprintf( '/sites/%d/unauth-file-upload/%s', $blog_id, $file_id );

$response = \Automattic\Jetpack\Connection\Client::wpcom_json_api_request_as_blog(
		$request_url,
		'v2',
		array(
			'method' => 'GET',
		),
		null,
		'wpcom'
	);

$file_content = wp_remote_retrieve_body( $response );

if ( is_wp_error( $response ) || empty( $file_content ) ) {
		return new \WP_Error( 'jetpack_unauth_file_upload_error', esc_html__( 'Error retrieving file content.', 'jetpack' ) );
	}

try {
		$content = json_decode( $file_content, true, 3, defined( 'JSON_THROW_ON_ERROR' ) ? \JSON_THROW_ON_ERROR : 0 ); // phpcs:ignore PHPCompatibility.Constants.NewConstants.json_throw_on_errorFound
		if ( isset( $content['message'] ) ) {
			return new \WP_Error( 'jetpack_unauth_file_upload_error', esc_html__( 'Error retrieving file content.', 'jetpack' ) );
		}
	} catch ( \Exception $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch
		// If the file is not JSON, we assume it's a binary file.
	}

$content_disposition = wp_remote_retrieve_header( $response, 'content-disposition' );
	$filename            = '';
	if ( $content_disposition ) {
		// Match the filename using a regular expression
		if ( preg_match( '/filename="([^"]+)"/', $content_disposition, $matches ) ) {
			$filename = $matches[1]; // Extract the filename
		}
	}

$type = wp_remote_retrieve_header( $response, 'content-type' );
	if ( empty( $type ) ) {
		$type = 'application/octet-stream'; // Default to binary if no content type is found
	}

return array(
		'content' => $file_content,
		'type'    => $type,
		'name'    => $filename,
	);
}

/**
 * Check which file type is previewable in the browser without downloading them.
 *
 * Allow images with extensions jpg, jpeg, png, gif, webp and pdf files.
 *
 * @param string $file_type The MIME type of the file.
 * @return bool True if the file is previable, false otherwise.
 */
function is_file_type_previewable( $file_type ) {
	$previable_types = array(
		'image/jpeg',
		'image/png',
		'image/gif',
		'image/webp',
		'application/pdf',
	);

return in_array( $file_type, $previable_types, true );
}

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Edit File: unauth-file-upload.php

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