unauth-file-upload.php
| 1 | <?php |
| 2 | /** |
| 3 | * Unauthenticated File Upload Helper Functions. |
| 4 | * |
| 5 | * @package automattic/jetpack |
| 6 | */ |
| 7 | |
| 8 | namespace Automattic\Jetpack\UnauthFileUpload; |
| 9 | |
| 10 | if ( ! defined( 'ABSPATH' ) ) { |
| 11 | exit( 0 ); |
| 12 | } |
| 13 | |
| 14 | add_action( 'wp_ajax_jetpack_unauth_file_download', __NAMESPACE__ . '\handle_file_download' ); |
| 15 | add_filter( 'jetpack_unauth_file_upload_get_file', __NAMESPACE__ . '\get_file_content', 10, 2 ); |
| 16 | add_filter( 'jetpack_unauth_file_download_url', __NAMESPACE__ . '\filter_get_download_url', 10, 2 ); |
| 17 | |
| 18 | /** |
| 19 | * The lifetime of a download link, in seconds. |
| 20 | * |
| 21 | * Kept generous enough that an editor returning to the responses dashboard days later still |
| 22 | * has a working link, short enough to limit the exposure of a leaked URL. |
| 23 | */ |
| 24 | const DOWNLOAD_LINK_LIFETIME = 7 * DAY_IN_SECONDS; |
| 25 | |
| 26 | /** |
| 27 | * The token scheme version carried in download links. |
| 28 | * |
| 29 | * Travels in the URL as `token_version` and is bound into the signature, so the signing scheme |
| 30 | * can be changed in the future (bump this and branch on the value in authorize_file_download()) |
| 31 | * without older links being mistaken for the new format. |
| 32 | */ |
| 33 | const DOWNLOAD_TOKEN_VERSION = 'v1'; |
| 34 | |
| 35 | /** |
| 36 | * Get the secret used to sign download links. |
| 37 | * |
| 38 | * Defaults to the Jetpack blog token, which this feature already depends on (the file content |
| 39 | * is fetched from WP.com as the blog). There is nothing extra to store, and reconnecting |
| 40 | * Jetpack rotates the token and so invalidates any outstanding links. Only the secret portion |
| 41 | * of the token (after the publicly-visible key prefix) is used, matching the rest of the |
| 42 | * connection stack. |
| 43 | * |
| 44 | * @since 16.0 |
| 45 | * |
| 46 | * @return string The signing key, or an empty string if no secret is available. |
| 47 | */ |
| 48 | function get_download_signing_key() { |
| 49 | $blog_token = ( new \Automattic\Jetpack\Connection\Tokens() )->get_access_token(); |
| 50 | $secret = ''; |
| 51 | |
| 52 | if ( $blog_token && ! is_wp_error( $blog_token ) && ! empty( $blog_token->secret ) ) { |
| 53 | // Blog tokens are stored as "key.secret"; sign with the secret part only, matching the |
| 54 | // rest of the connection stack. Require exactly two non-empty parts so a malformed token |
| 55 | // fails closed rather than signing links the fetch path could never honor. |
| 56 | $parts = explode( '.', (string) $blog_token->secret, 2 ); |
| 57 | if ( count( $parts ) === 2 && '' !== $parts[0] && '' !== $parts[1] ) { |
| 58 | $secret = $parts[1]; |
| 59 | } |
| 60 | } |
| 61 | |
| 62 | /** |
| 63 | * Filters the secret used to sign Forms unauthenticated file-download links. |
| 64 | * |
| 65 | * Defaults to the Jetpack blog token secret. Environments without a usable blog token |
| 66 | * (e.g. WordPress.com Simple) can return their own stable, secret value here so that |
| 67 | * download links can still be signed and verified. |
| 68 | * |
| 69 | * @since 16.0 |
| 70 | * |
| 71 | * @param string $secret The signing secret. Empty string if none is available. |
| 72 | */ |
| 73 | return (string) apply_filters( 'jetpack_unauth_file_download_signing_key', $secret ); |
| 74 | } |
| 75 | |
| 76 | /** |
| 77 | * Generate a signed token authorizing the download of a given file. |
| 78 | * |
| 79 | * Unlike a WordPress nonce, the token is not tied to a specific user or session, so a link |
| 80 | * generated by one logged-in editor works for any logged-in editor. The expiry timestamp is |
| 81 | * part of the signed payload, so it cannot be tampered with to extend access. |
| 82 | * |
| 83 | * @since 16.0 |
| 84 | * |
| 85 | * @param int $file_id The file ID. |
| 86 | * @param int $expires Unix timestamp at which the link stops being valid. |
| 87 | * @param string $version The token scheme version. Defaults to the current scheme. |
| 88 | * |
| 89 | * @return string The hex-encoded HMAC-SHA256 token, or an empty string if there is no signing key. |
| 90 | */ |
| 91 | function generate_download_token( $file_id, $expires, $version = DOWNLOAD_TOKEN_VERSION ) { |
| 92 | $key = get_download_signing_key(); |
| 93 | |
| 94 | if ( '' === $key ) { |
| 95 | return ''; |
| 96 | } |
| 97 | |
| 98 | $payload = 'jetpack_unauth_file_download|' . $version . '|' . (int) $file_id . '|' . (int) $expires; |
| 99 | return hash_hmac( 'sha256', $payload, $key ); |
| 100 | } |
| 101 | |
| 102 | /** |
| 103 | * Verify a download token against the expected signature using a constant-time comparison. |
| 104 | * |
| 105 | * Expiry is checked separately by the caller so it can surface a distinct "expired" message. |
| 106 | * Fails closed when no signing key is available (i.e. the site is not connected). |
| 107 | * |
| 108 | * @since 16.0 |
| 109 | * |
| 110 | * @param int $file_id The file ID. |
| 111 | * @param int $expires Unix timestamp the token was signed with. |
| 112 | * @param string $token The token supplied in the request. |
| 113 | * @param string $version The token scheme version the token was signed with. |
| 114 | * |
| 115 | * @return bool True if the token matches. |
| 116 | */ |
| 117 | function verify_download_token( $file_id, $expires, $token, $version = DOWNLOAD_TOKEN_VERSION ) { |
| 118 | $expected = generate_download_token( $file_id, $expires, $version ); |
| 119 | |
| 120 | return '' !== $expected |
| 121 | && is_string( $token ) && '' !== $token |
| 122 | && hash_equals( $expected, $token ); |
| 123 | } |
| 124 | |
| 125 | /** |
| 126 | * Get the file download URL filter callback. |
| 127 | * |
| 128 | * @param string $url The file download URL. |
| 129 | * @param int $file_id The file ID. |
| 130 | * |
| 131 | * @return string The file download URL. |
| 132 | */ |
| 133 | function filter_get_download_url( $url, $file_id ) { |
| 134 | $expires = time() + DOWNLOAD_LINK_LIFETIME; |
| 135 | $token = generate_download_token( $file_id, $expires ); |
| 136 | |
| 137 | if ( '' === $token ) { |
| 138 | // No signing key (disconnected site, or WP.com Simple without the signing-key filter |
| 139 | // wired). Return the passthrough so callers omit the link instead of handing out one |
| 140 | // that can never work, and leave a breadcrumb for operators. |
| 141 | error_log( 'Jetpack Forms: unable to sign file download link; no signing key available.' ); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log |
| 142 | return $url; |
| 143 | } |
| 144 | |
| 145 | return add_query_arg( |
| 146 | array( |
| 147 | 'action' => 'jetpack_unauth_file_download', |
| 148 | 'file_id' => $file_id, |
| 149 | 'expires' => $expires, |
| 150 | 'token_version' => DOWNLOAD_TOKEN_VERSION, |
| 151 | 'token' => $token, |
| 152 | ), |
| 153 | admin_url( 'admin-ajax.php' ) |
| 154 | ); |
| 155 | } |
| 156 | |
| 157 | /** |
| 158 | * Reject a download request with the generic invalid-link error and a debug code, then exit. |
| 159 | * |
| 160 | * The message stays generic so it leaks nothing to the requester and stays actionable (a token |
| 161 | * can be rejected simply because the blog token rotated on reconnect), while the appended code |
| 162 | * identifies which check failed, so a user-reported screenshot is enough to locate the cause: |
| 163 | * |
| 164 | * 1 - Missing or unrecognized token_version. |
| 165 | * 2 - Token signature did not verify. |
| 166 | * 3 - Legacy nonce did not verify. |
| 167 | * 4 - No token and no legacy nonce supplied. |
| 168 | * |
| 169 | * @since 16.0 |
| 170 | * |
| 171 | * @param int $code Number identifying the failing check. |
| 172 | * |
| 173 | * @return void Terminates the request via wp_die(). |
| 174 | */ |
| 175 | function invalid_download_link( $code ) { |
| 176 | wp_die( |
| 177 | esc_html( |
| 178 | sprintf( |
| 179 | /* translators: %d: error code used for debugging. */ |
| 180 | __( 'This download link is no longer valid. Reload the responses page to get a fresh link. (%d)', 'jetpack' ), |
| 181 | (int) $code |
| 182 | ) |
| 183 | ), |
| 184 | '', |
| 185 | array( 'response' => 403 ) |
| 186 | ); |
| 187 | } |
| 188 | |
| 189 | /** |
| 190 | * Authorize a download request and return the requested file ID. |
| 191 | * |
| 192 | * Holds the security-critical gate (capability check, then either the current signed-token |
| 193 | * scheme or the legacy nonce fallback). Terminates the request via wp_die() on any failure and |
| 194 | * only returns when the caller is allowed to download the file. Kept separate from the |
| 195 | * file-serving logic in handle_file_download() so each branch is unit-testable without the |
| 196 | * headers/exit of the serving path. |
| 197 | * |
| 198 | * @since 16.0 |
| 199 | * |
| 200 | * @return int The validated file ID. |
| 201 | */ |
| 202 | function authorize_file_download() { |
| 203 | if ( ! current_user_can( 'edit_pages' ) ) { |
| 204 | wp_die( esc_html__( 'Sorry, you are not allowed to access this page.', 'jetpack' ), '', array( 'response' => 403 ) ); |
| 205 | } |
| 206 | |
| 207 | $file_id = isset( $_GET['file_id'] ) ? absint( wp_unslash( $_GET['file_id'] ) ) : 0; |
| 208 | |
| 209 | if ( ! $file_id ) { |
| 210 | wp_die( esc_html__( 'Invalid file request.', 'jetpack' ), '', array( 'response' => 400 ) ); |
| 211 | } |
| 212 | |
| 213 | $token = isset( $_GET['token'] ) ? sanitize_text_field( wp_unslash( $_GET['token'] ) ) : ''; |
| 214 | |
| 215 | if ( '' !== $token ) { |
| 216 | // Current scheme: a site-signed, expiring token. Future schemes can branch on the version. |
| 217 | $token_version = isset( $_GET['token_version'] ) ? sanitize_text_field( wp_unslash( $_GET['token_version'] ) ) : ''; |
| 218 | |
| 219 | if ( DOWNLOAD_TOKEN_VERSION !== $token_version ) { |
| 220 | invalid_download_link( 1 ); |
| 221 | } |
| 222 | |
| 223 | $expires = isset( $_GET['expires'] ) ? absint( wp_unslash( $_GET['expires'] ) ) : 0; |
| 224 | |
| 225 | // A link is valid up to and including its expiry second; expired once time passes it. |
| 226 | if ( ! $expires || $expires < time() ) { |
| 227 | wp_die( esc_html__( 'This download link has expired. Reload the responses page to get a fresh link.', 'jetpack' ), '', array( 'response' => 410 ) ); |
| 228 | } |
| 229 | |
| 230 | // $token_version was asserted equal to DOWNLOAD_TOKEN_VERSION above; pass the constant so |
| 231 | // a future multi-version branch can't accidentally feed the request value back in. |
| 232 | if ( ! verify_download_token( $file_id, $expires, $token, DOWNLOAD_TOKEN_VERSION ) ) { |
| 233 | invalid_download_link( 2 ); |
| 234 | } |
| 235 | } elseif ( isset( $_GET['_wpnonce'] ) ) { |
| 236 | /* |
| 237 | * Backward compatibility for legacy per-file nonce links that may still be circulating |
| 238 | * in already-sent emails. WordPress nonces are only valid for ~24h, so these links |
| 239 | * expire on their own shortly after the signed-token scheme ships. |
| 240 | * |
| 241 | * @todo Remove this legacy nonce fallback in Jetpack 16.3 or later; links signed under |
| 242 | * the old scheme self-expire within ~24h of the signed-token scheme shipping. |
| 243 | */ |
| 244 | if ( ! wp_verify_nonce( sanitize_text_field( wp_unslash( $_GET['_wpnonce'] ) ), 'jetpack_unauth_file_download_nonce_' . $file_id ) ) { |
| 245 | invalid_download_link( 3 ); |
| 246 | } |
| 247 | } else { |
| 248 | invalid_download_link( 4 ); |
| 249 | } |
| 250 | |
| 251 | return $file_id; |
| 252 | } |
| 253 | |
| 254 | /** |
| 255 | * Handle file download requests from the admin page. |
| 256 | * |
| 257 | * @return never This method never returns as it exits directly |
| 258 | */ |
| 259 | function handle_file_download() { |
| 260 | $file_id = authorize_file_download(); |
| 261 | |
| 262 | /** |
| 263 | * Get the file content that we send to the user to download. |
| 264 | * |
| 265 | * @since 14.6 |
| 266 | * |
| 267 | * @param array $file_content The file content. |
| 268 | * @param string $file_id The file ID. |
| 269 | * |
| 270 | * @return array|\WP_Error The file array, containing the content, name and type. |
| 271 | */ |
| 272 | $file = apply_filters( 'jetpack_unauth_file_upload_get_file', array(), $file_id ); |
| 273 | |
| 274 | if ( is_wp_error( $file ) || empty( $file ) || ! is_array( $file ) ) { |
| 275 | wp_die( esc_html__( 'Error retrieving file content.', 'jetpack' ) ); |
| 276 | } |
| 277 | |
| 278 | // Given $file can be manipulated by a filter, make sure everything is as it should be. |
| 279 | $file['content'] = $file['content'] ?? ''; |
| 280 | $file['type'] = $file['type'] ?? 'application/octet-stream'; |
| 281 | $file['name'] = $file['name'] ?? ''; |
| 282 | |
| 283 | // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- The request is already authorized in authorize_file_download() before reaching here. |
| 284 | $is_preview = isset( $_GET['preview'] ) && 'true' === $_GET['preview'] && is_file_type_previewable( $file['type'] ); |
| 285 | |
| 286 | // Clean output buffer |
| 287 | if ( ob_get_length() ) { |
| 288 | ob_clean(); |
| 289 | } |
| 290 | // Set headers for download |
| 291 | header( 'Content-Type: ' . $file['type'] ); |
| 292 | |
| 293 | if ( ! $is_preview ) { |
| 294 | // Forcing the file to be downloaded is important to prevent XSS attacks. |
| 295 | header( 'Content-Disposition: attachment; filename="' . sanitize_file_name( $file['name'] ) . '"' ); |
| 296 | } else { |
| 297 | // For preview mode, use inline disposition |
| 298 | header( 'Content-Disposition: inline; filename="' . sanitize_file_name( $file['name'] ) . '"' ); |
| 299 | } |
| 300 | header( 'Content-Length: ' . strlen( $file['content'] ) ); |
| 301 | header( 'Content-Transfer-Encoding: binary' ); |
| 302 | header( 'Cache-Control: no-cache, must-revalidate, max-age=0' ); |
| 303 | header( 'Pragma: no-cache' ); |
| 304 | header( 'Expires: 0' ); |
| 305 | |
| 306 | // Output file content and exit |
| 307 | echo $file['content']; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Binary file data |
| 308 | exit( 0 ); |
| 309 | } |
| 310 | |
| 311 | /** |
| 312 | * Get the file content. |
| 313 | * |
| 314 | * @param array $file_content The file content, name and type. |
| 315 | * @param integer $file_id The file ID. |
| 316 | * @return array|\WP_Error The file content, name and type |
| 317 | */ |
| 318 | function get_file_content( $file_content, $file_id ) { |
| 319 | if ( ( new \Automattic\Jetpack\Status\Host() )->is_wpcom_simple() ) { |
| 320 | return $file_content; |
| 321 | } |
| 322 | |
| 323 | $blog_id = \Jetpack_Options::get_option( 'id' ); |
| 324 | $request_url = sprintf( '/sites/%d/unauth-file-upload/%s', $blog_id, $file_id ); |
| 325 | |
| 326 | $response = \Automattic\Jetpack\Connection\Client::wpcom_json_api_request_as_blog( |
| 327 | $request_url, |
| 328 | 'v2', |
| 329 | array( |
| 330 | 'method' => 'GET', |
| 331 | ), |
| 332 | null, |
| 333 | 'wpcom' |
| 334 | ); |
| 335 | |
| 336 | $file_content = wp_remote_retrieve_body( $response ); |
| 337 | |
| 338 | if ( is_wp_error( $response ) || empty( $file_content ) ) { |
| 339 | return new \WP_Error( 'jetpack_unauth_file_upload_error', esc_html__( 'Error retrieving file content.', 'jetpack' ) ); |
| 340 | } |
| 341 | |
| 342 | try { |
| 343 | $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 |
| 344 | if ( isset( $content['message'] ) ) { |
| 345 | return new \WP_Error( 'jetpack_unauth_file_upload_error', esc_html__( 'Error retrieving file content.', 'jetpack' ) ); |
| 346 | } |
| 347 | } catch ( \Exception $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch |
| 348 | // If the file is not JSON, we assume it's a binary file. |
| 349 | } |
| 350 | |
| 351 | $content_disposition = wp_remote_retrieve_header( $response, 'content-disposition' ); |
| 352 | $filename = ''; |
| 353 | if ( $content_disposition ) { |
| 354 | // Match the filename using a regular expression |
| 355 | if ( preg_match( '/filename="([^"]+)"/', $content_disposition, $matches ) ) { |
| 356 | $filename = $matches[1]; // Extract the filename |
| 357 | } |
| 358 | } |
| 359 | |
| 360 | $type = wp_remote_retrieve_header( $response, 'content-type' ); |
| 361 | if ( empty( $type ) ) { |
| 362 | $type = 'application/octet-stream'; // Default to binary if no content type is found |
| 363 | } |
| 364 | |
| 365 | return array( |
| 366 | 'content' => $file_content, |
| 367 | 'type' => $type, |
| 368 | 'name' => $filename, |
| 369 | ); |
| 370 | } |
| 371 | |
| 372 | /** |
| 373 | * Check which file type is previewable in the browser without downloading them. |
| 374 | * |
| 375 | * Allow images with extensions jpg, jpeg, png, gif, webp and pdf files. |
| 376 | * |
| 377 | * @param string $file_type The MIME type of the file. |
| 378 | * @return bool True if the file is previable, false otherwise. |
| 379 | */ |
| 380 | function is_file_type_previewable( $file_type ) { |
| 381 | $previable_types = array( |
| 382 | 'image/jpeg', |
| 383 | 'image/png', |
| 384 | 'image/gif', |
| 385 | 'image/webp', |
| 386 | 'application/pdf', |
| 387 | ); |
| 388 | |
| 389 | return in_array( $file_type, $previable_types, true ); |
| 390 | } |
| 391 |