Proxy with NTLM authentication

Many large Corporates are using Proxys with NTLM authentication which gives you trouble on Linux because
applications like pip, git, wget, cpan, lynx or even apt do NOT support NLTM authentication.

The solution to mitigate can be cntlm,
a tiny proxy tool which sits on localhost between the client application and the corporate proxy.

This wiki is about to explain how to setup cntlm.

Install cntlm on Debian/Ubuntu

apt-get install cntlm

Configure cntlm

Create Password Hashes

cntlm supports password hashes which is strongly recommend to use,

• Create Password Hash:

# cntlm -H -d domain.com -u username
Password:
PassLM          48A840A3F27888D0552C4BCA4AEBFB11
PassNT          831DE0E83F51180463145ACD2FAB9529
PassNTLMv2      ACDA91797DCFDAF15CFE369C2EE28AE9    # Only for user 'username', domain 'domain.com'

Setup the cntlm configuration:

• Edit configuration (/etc/cntlm.conf):

# nano /etc/cntlm.conf

• Sample configuration (/etc/cntlm.conf):

Username        username
Domain          domain.com
Proxy           wwwproxy.corp.com:8080
NoProxy         localhost, 127.0.0.*, 10.*, 192.168.*
Listen          3128
#Paste the above user credentials into here
PassLM          48A840A3F27888D0552C4BCA4AEBFB11
PassNT          831DE0E83F51180463145ACD2FAB9529
PassNTLMv2      ACDA91797DCFDAF15CFE369C2EE28AE9    # Only for user 'username', domain 'domain.com'

Operating cntlm

Use SystemD to control, tested on Debian11 and Ubuntu22

# systemctl status cntlm
# systemctl stop cntlm 
# systemctl start cntlm
# systemctl disable cntlm
# systemctl enable cntlm

Check cntlm

• Check for an open port, note that 127.0.0.1:3128 should be used instead of 0.0.0.0:3128 (gateway mode)

# netstat -tpan | grep 3128
tcp        0      0 127.0.0.1:3128          0.0.0.0:*               LISTEN      1622441/cntlm

• Check syslog

# tail -n 5000 /var/log/syslog | grep cntlm

• Check process

# ps -e | grep cntlm

Test cntlm

• Try without giving a password

# cntlm -M http://google.com
Password:
Config profile  1/4... OK (HTTP code: 301)
----------------------------[ Profile  0 ]------
Auth            NTLMv2
PassNTLMv2      4A3FCA2104D7B7B9683DB7472279XXXX
------------------------------------------------

Set Linux environment

export https_proxy=http://127.0.0.1:3128
export http_proxy=http://127.0.0.1:3128

Set APT environment

• /etc/apt/apt.conf

Acquire::http::Proxy "http://127.0.0.1:3128";

Finalize

Tools such as

• apt, apt-get, dpkg
• pip
• git
• cpan
• curl
• wget
• lynx

should now work without any proxy params