Description:
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It is possible to overwrite the contents of $_REQUEST_URI with a uri longer than 16400 bytes. It allows a attacker to manipulate the global variable in unexpected ways. It has low impact as it only related to the build in server.

Test script:
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Create a file named testtest1.php with the following content
<a href="<?= $_SERVER['REQUEST_URI'] ?>">Unexpected url</a>

Start the buildin php server 
php -S localhost:8090

Go to the browser and execute the following script in the console
window.location.href = (url ='http://testtest1.php:8090/overflow.php?')+("x".repeat(16400-url.length)+"//example.com");

it changes the url to "http://testtest1:8090/overflow.php?[16365 x here][payload]

Expected result:
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localhost:8090 + a long string

Actual result:
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example.com