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To: Raymond Irving <xwisdom@gmail.com>,
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Cc: bishop@php.net
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Date: Sun, 14 Apr 2019 14:47:18 -0700
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Subject: Re: [PHP-DEV] PHP deserialization techniques offer rich pickings for
 security researchers
From: smalyshev@gmail.com (Stanislav Malyshev)

Hi!

> I came across this article which highlights a few issues with PHP
> deserialization techniques:
> 
> https://portswigger.net/daily-swig/phar-out-php-deserialization-techniques-offer-rich-pickings-for-security-researchers

PHP serialization is not meant to be used with external or
user-modifyable data. Looks like the crux of the issue is that phar uses
unserialize() to read metadata, which is an insecure scenario since it
is common to deal with external phar files and it's not obvious there
can be serialized data. Particular Drupal exploit seems to be caused by
insecure coding (one should not be able to give phar streams to system
paths) but the general issue of reading phars being insecure stays.

It is a bit problematic since there are no limitations in what can be
stored in Phar metadata, so we can't really prohibit anything there
without breaking BC. I would start with banning objects there (at least
by default) but that again would be BC break if somebody did use objects
there. More workable idea would be to not parse metadata unless
getMetadata() is explicitly called. The chance of code that did not
intend to use metadata to use this call is nil, thus eliminating the
deserialization vector in most cases. OTOH, BC is kept since the
metadata is still available for the code that needs it. I'll try to
implement this soon.
-- 
Stas Malyshev
smalyshev@gmail.com