Req #69450 [Wfx]: Default to ENT_SUBSTITUTE for htmlspecialchars()

Edit report at https://bugs.php.net/bug.php?id=69450&edit=1 ID: 69450 User updated by: olafvdspek at gmail dot com Reported by: olafvdspek at gmail dot com Summary: Default to ENT_SUBSTITUTE for htmlspecialchars() Status: Wont fix Type: Feature/Change Request Package: Output Control PHP Version: Irrelevant Block user comment: N Private report: N New Comment: @Rasmus: Why does it not log an error and why does it not halt execution? Previous Comments: ------------------------------------------------------------------------ [2015-04-15 06:28:51] rasmus@php.net Yes, from a security perspective, trying to fix a broken byte stream with any sort of guesses and replacement characters is a non-starter. You simply don't do it. Certainly not by default. If someone really wants to try to fix broken input they need to do so explicitly and hopefully they understand the risk they are taking. The most common example char replacement problems is Internet Explorer doing substitution on broken UTF8 in IE5 and IE6. For example, something like %E0%22%3E which is byte 0xE0 followed by " and > would get substituted with a �. So what you say? Well, by swallowing the "> you have yourself a glaring XSS since all subsequent characters are now no longer inside a quoted parameter in a tag. And IE replaced those 3 bytes because the E0 byte is the start of a 3-byte UTF8 sequence, so a user could XSS IE simply by adding a %E0 to GET/POST data. ------------------------------------------------------------------------ [2015-04-15 05:52:09] yohgaki@php.net I should have post undebatable example. Anyway, don't forget there is encoding includes "\" in multibyte stream. ------------------------------------------------------------------------ [2015-04-15 05:49:08] yohgaki@php.net More detailed example. <multibyte start byte> + "<" What should happen? Replace <multibyte start byte>? or Replace <multibyte start byte> + "<"? Neither is correct and will break structured text. ------------------------------------------------------------------------ [2015-04-15 05:45:16] yohgaki@php.net Generally speaking, escape functions cannot determine if a invalid byte in multibyte stream is legitimate or not. Besides, invalid multibyte stream should be detected while input data handling. This is the best practice. Otherwise, apps may be affected by char encoding based attack any places in the software including low level lib's vulnerability. BTW, current chrome (since about 2 years ago) won't output any if input is broken badly because it's impossible to make sure security. Returning blank string perfectly makes sense for security stand point. ------------------------------------------------------------------------ [2015-04-14 20:28:13] nikic@php.net I also think that ENT_SUBSTITUTE is a more reasonable default behavior. Could you elaborate in which circumstances it will cause broken output? ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=69450 -- Edit this bug report at https://bugs.php.net/bug.php?id=69450&edit=1