Bug #54114 [Com]: Output Buffer Dumps Data On Error

Edit report at https://bugs.php.net/bug.php?id=54114&edit=1 ID: 54114 Comment by: nicolas dot grekas+php at gmail dot com Reported by: danhstevens at gmail dot com Summary: Output Buffer Dumps Data On Error Status: Open Type: Bug Package: Output Control Operating System: all PHP Version: 5.3.5 Block user comment: N Private report: N New Comment: Here is an other example that can't be workaround using danhstevens' technique: <?php function my_shutdown() { echo "secret\n"; throw new Exception; } function ob_custom_filter($b) { return str_replace('secret', '******', $b); } register_shutdown_function('my_shutdown'); ob_start('ob_custom_filter'); ?> Previous Comments: ------------------------------------------------------------------------ [2011-03-10 19:41:28] danhstevens at gmail dot com I've found a viable work-around for this bug (although a patch of the core would still be ideal so people don't discover this potential security issue the hard-way). By registering the following shutdown handler before any output buffering the dump of data can be prevented: <?php function shutdown_fn() { //If ob_start has been called at least once if(ob_get_level() > 1) { //Prevent data in buffer from dumping ob_end_clean(); } } register_shutdown_function('shutdown_fn'); Now when using the examples above that normally cause the buffer to dump to the client the buffer data is disposed of. Of course, this can be extended to use ob_get_contents and redirect the data to file or other means if necessary. This approach is working for me (on PHP 5.3.5). ~Dan ------------------------------------------------------------------------ [2011-03-06 16:51:52] neweracracker at gmail dot com I've managed to reproduce this in Windows 7 running php 5.2.17 (with php.ini-dist) and php 5.3.5 (with php.ini-development). Here is my test script: <?php set_time_limit(1); ob_start(); echo "You shouldn't see this!"; sleep(2); //comment this and you won't see the line above in output ;) ob_end_clean(); ?> I've reported this as bug #54174 which got closed due being a dupe of this one so I am leaving this comment here for reference purposes. Regards, NewEraCracker. ------------------------------------------------------------------------ [2011-02-28 21:40:36] danhstevens at gmail dot com Hi Rasmus, I was still able to create the problem by calling on a non-existing class to create a fatal error. Here is a variation of your code: function eh($errno, $errstr, $errfile, $errline) { $contents = ob_get_contents(); ob_end_clean(); echo "Error: $errno, $errstr, $errfile, $errline\n"; } set_error_handler('eh'); ob_start(); echo 123; nonExistantClass::nonExistantMethod(); echo "After error\n"; Output is: 123 Fatal error: Class 'nonExistantClass' not found in ... Hopefully the above should more accurately illustrate the issue. ------------------------------------------------------------------------ [2011-02-28 19:37:32] rasmus@php.net I am unable to reproduce this. My test script: <?php function eh($errno, $errstr, $errfile, $errline) { $contents = ob_get_contents(); ob_end_clean(); echo "Error: $errno, $errstr, $errfile, $errline\n"; } set_error_handler('eh'); ob_start(); echo 123; trigger_error('test error', E_USER_ERROR); echo "After error\n"; And my output is: Error: 256, test error, /var/www/testing/o.php, 10 After error No sign of "123" there. ------------------------------------------------------------------------ [2011-02-28 07:43:46] danhstevens at gmail dot com Description: ------------ When output buffering is turned on (via ob_start()) and an error is encountered before a call to ob_end_* is called the entire contents of the output buffer is dumped (to STDOUT) and there appears to be no way to prevent the buffer from dumping - not even by setting an error handler, etc. This is a security issue since the output buffer may contain sensitive information that is them dumped over to the user. Using set_error_handler does not stop the dump - it appears the dump simply happens with no way to intercept or prevent it. Test script: --------------- <?php ob_start(); echo 123; trigger_error('test error', E_USER_ERROR); $contents = ob_get_contents(); ob_end_clean(); ?> Expected result: ---------------- (no output) Actual result: -------------- 123 Fatal error: test error in ... ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=54114&edit=1