Description:
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It is opened as bug for possible future reference only. It occurred after running command to get php-apc installed after enabling Zend OpCache from php.ini for emulation of our one blog reader's problem.  Other packages were -  php5-xcache and php5-apcu. php -v command vanished xcache's name in output and zend opcache pointed towards an invalid pointer error.

We have added a PHP script to get 500 internal server error. Setup with such wrong steps will work fine, but possibly it is a risk to allow such unnoticed error.


Unexpected output :

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root@4gbtcw:/home/ubuntu# php -v
PHP Warning:  Module 'Zend OPcache' already loaded in Unknown on line 0
PHP Warning:  Zend OPcache: module registration failed! in Unknown on line 0
PHP 5.5.9-1ubuntu4.13 (cli) (built: Sep 29 2015 15:24:49)
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2014 Zend Technologies
    with Zend OPcache v7.0.3, Copyright (c) 1999-2014, by Zend Technologies
*** Error in `php': free(): invalid pointer: 0x00007fb8003ff0e0 ***
Aborted (core dumped)

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Test script:
---------------
repo has test.php file and backtrace - https://github.com/AbhishekGhosh/invalid-pointer-0x00007f75ec3ff0e0

Expected result:
----------------
test.php will show 500 internal server error on curl. 

Actual result:
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Above URL of the repo has detailed output. Possibly not required unless demanded for finding any security flaw. 
OpenStack snapshot of the instance with the issue can be asked from us - https://thecustomizewindows.com/