CVE-2024-46483 - Pre-Authentication Heap Overflow in Xlight SFTP server
Xlight 32 and 64-bit versions <= 3.9.4.2
FTP Bounce attack
Consider we are targetting an FTP Server FTP_DMZ exposed to the internet. Another device within the same network, Internal_DMZ, is not exposed to the internet. We can use the connection to the FTP_DMZ server to scan Internal_DMZ using the FTP Bounce attack and obtain information about the server's open ports. Then, we can use that information as part of our attack against the infrastructure.
The Nmap -b flag can be used to perform an FTP bounce attack:
$ nmap -Pn -v -n -p80 -b anonymous:password@10.10.110.213 172.17.0.2
Starting Nmap 7.80 ( https://nmap.org ) at 2020-10-27 04:55 EDT
Resolved FTP bounce attack proxy to 10.10.110.213 (10.10.110.213).
Attempting connection to ftp://anonymous:password@10.10.110.213:21
Connected:220 (vsFTPd 3.0.3)
Login credentials accepted by FTP server!
Initiating Bounce Scan at 04:55
FTP command misalignment detected ... correcting.
Completed Bounce Scan at 04:55, 0.54s elapsed (1 total ports)
Nmap scan report for 172.17.0.2
Host is up.
PORT STATE SERVICE
80/tcp open http
<SNIP>
lftp
lftp :~> set ftp:ssl-force true
lftp :~> set ssl:verify-certificate no
lftp :~> connect 10.10.10.208
lftp 10.10.10.208:~> login
Usage: login <user|URL> [<pass>]
lftp 10.10.10.208:~> login username Password
Theory
A distinction is made between active and passive FTP. In the active variant, the client establishes the connection as described via TCP port 21 and thus informs the server via which client-side port the server can transmit its responses. However, if a firewall protects the client, the server cannot reply because all external connections are blocked. For this purpose, the passive mode has been developed. Here, the server announces a port through which the client can establish the data channel. Since the client initiates the connection in this method, the firewall does not block the transfer.
Commands
Commands:
bye
cd
close
Exits from FTP.
delete
dir
disconnect
Exits from FTP.
get
Grabs file from the connected computer.
put
Send one file.
pwd
Configuration
cat /etc/vsftpd.conf | grep -v "#"
Setting
Description
listen=NO
Run from inetd or as a standalone daemon?
listen_ipv6=YES
Listen on IPv6 ?
anonymous_enable=NO
Enable Anonymous access?
local_enable=YES
Allow local users to login?
dirmessage_enable=YES
Display active directory messages when users go into certain directories?
use_localtime=YES
Use local time?
xferlog_enable=YES
Activate logging of uploads/downloads?
connect_from_port_20=YES
Connect from port 20?
secure_chroot_dir=/var/run/vsftpd/empty
Name of an empty directory
pam_service_name=vsftpd
This string is the name of the PAM service vsftpd will use.
0xss0rz@htb[/htb]$ wget -m --no-passive ftp://anonymous:anonymous@10.129.14.136
--2021-09-19 14:45:58-- ftp://anonymous:*password*@10.129.14.136/
=> ‘10.129.14.136/.listing’
Connecting to 10.129.14.136:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done. ==> PWD ... done.
==> TYPE I ... done. ==> CWD not needed.
==> PORT ... done. ==> LIST ... done.
12.12.1.136/.listing [ <=> ] 466 --.-KB/s in 0s
2021-09-19 14:45:58 (65,8 MB/s) - ‘10.129.14.136/.listing’ saved [466]
--2021-09-19 14:45:58-- ftp://anonymous:*password*@10.129.14.136/Calendar.pptx
=> ‘10.129.14.136/Calendar.pptx’
==> CWD not required.
==> SIZE Calendar.pptx ... done.
==> PORT ... done. ==> RETR Calendar.pptx ... done.
...SNIP...
2021-09-19 14:45:58 (48,3 MB/s) - ‘10.129.14.136/Employees/.listing’ saved [119]
FINISHED --2021-09-19 14:45:58--
Total wall clock time: 0,03s
Downloaded: 15 files, 1,7K in 0,001s (3,02 MB/s)
Upload a File
ftp> put testupload.txt
local: testupload.txt remote: testupload.txt
---> PORT 10,10,14,4,184,33
200 PORT command successful. Consider using PASV.
---> STOR testupload.txt
150 Ok to send data.
226 Transfer complete.
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from FTP.
Changes .
a file.
Lists files if connected.
dir -C lists the files in wide format.
dir -1 lists the files in bare format in order
dir -r lists directory in reverse alphabetic order.
dir -R lists all files in current directory and subdirectories.
dir -S lists files in bare format in alphabetic order.
Print .
A guide to simulating an internal security breach. You’ll take on the role of the attacker and work through every stage of a professional pentest, from information gathering to seizing control of a system and owning the network.
The book offers one of the most complete and in-depth analyses of Wi-Fi and Bluetooth networks, then progresses through the various protocols such as DNS, ARP, SMTP, and others.
