Description:
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When calling finfo::buffer() with a crafted string, PHP tries to allocate an insane amount of memory to do so. I found a similar bug here - https://bugs.php.net/bug.php?id=68819

I suspect the bug may have been re-introduced at some stage during newer versions.

1) I tested it on the version my customer had been using - v7.0.33 (doesn't work)
2) I then tested on the latest php version - v7.4.0 (doesn't work)
3) Testing on an older version - v5.4.16 it works perfectly.

Test script:
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Generated a random file of 300MB using:
      $ sudo fallocate -l 300M test-file

The script used:

        <?php
	$content = file_get_contents('test-file', true);
	$fileInfo = new \finfo(FILEINFO_MIME_TYPE);
	var_dump($fileInfo->buffer($content));
	?>

Expected result:
----------------
To provide the file metadata (I know there are other ways to do this):

string(19) "application/x-empty"

Actual result:
--------------
PHP Warning:  finfo::buffer(): Failed identify data 12:cannot allocate 2516582408 bytes (Cannot allocate memory)application/octet-stream in php shell code on line 1 bool(false)