Date: Tue, 19 May 2015 16:20:15 +0200 From: Andrea Palazzo <andrea.palazzo@...el.it> To: Stanislav Malyshev <smalyshev@...il.com> CC: oss-security@...ts.openwall.com, security@....net Subject: Re: CVE Request + Advisory: PHP str_repeat() sign mismatch based memory corruption Hi again! My point is: once you get to have a corrupted zval, there are tons of functions that would result in memory errors if working on it. A str_repeat() with user-supplied arguments is not so common at all, but let's say you have it (e.g. http://phpcrossref.com/xref/jpegmeta/EXIF.php.html, https://code.google.com/p/zimbra-api-php/, http://phpcrossref.com/xref/jpegmeta/XML.php.html) it is really likely that it would end up processed by one of these functions (string concatenation, for example). $makernote <http://phpcrossref.com/xref/jpegmeta/_variables/makernote.html> .=str_repeat <http://phpcrossref.com/xref/jpegmeta/_functions/str_repeat.html>("\x00",($tiff_data <http://phpcrossref.com/xref/jpegmeta/_variables/tiff_data.html>[ 'Makernote_Tag' ][ 'Offset' ] - 8 ) ); On 19/05/2015 00:43, Stanislav Malyshev wrote: > Hi! > >> About code execution, I haven't had the chance to focus on actual >> exploitation yet (I surely will in the near future), but as you can see >> from the original report (https://bugs.php.net/bug.php?id=69403), I >> pointed out several cases in which working on a so-crafted zval would >> lead to invalid memory access (with user controlled values as well), so >> I am pretty confident it is achievable. > These examples all seem to require specific code (like > 'md5(str_repeat("a", 4294967294-1));') to be run. The probability that > applications would contain this specific code with str_repeat argument > controlled by remote user seems to be pretty low. However, if you can > show exploiting this on a code of an application that is not specially > crafted to demonstrate this issue, or at least resembles code that is > likely to be deployed in a real application, I will gladly change my > opinion. >
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