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PHP/FI Buffer Overflow Vulnerability

The PHP/FI package which was originally written by Rasmus Lerdorf is an is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly.

Since it's inception PHP/FI has been turned over to another development team and is now known only as PHP. Certain versions of PHP/FI had a buffer overflow which could be triggered by a remote user to gain access to the web server running PHP/FI as the UID of the http daemon.

This buffer overflow was in the function FixFilename() function in file.c, PHP attempted to pass strings whose length may be as long as 8 kilobytes into buffers as small as 128 bytes. This overwrote the stack, making it possible for an attacker to obtain shell access to the machine running the web server.