Fix the OpenSSL Logjam issue on UNIX systems

September 11, 2015

By Gratien D'haese (gratien)

Fix the OpenSSL Logjam issue on UNIX systems Logjam is the name describing an attack on TLS connections using Diffie-Hellman ciphersuites (see article “Logjam, FREAK and Upcoming Changes in OpenSSL” for the details).

I was asked to write a script, which should be able to run on Linux, HP-UX and SunOS, to trace the vulnerability and fix it on the spot. It became a simple straightforward Korn shell script, which as you probably know is very portable to other UNIXes (feedback or pull request are always welcome).

The script has a basic help functionality:

#-> /home/gdhaese1/bin/fix-TLS-Logjam-vulnerability.sh -h
    Usage: fix-TLS-Logjam-vulnerability.sh [-m <mail1,mail2>] [-hv]
            -m: The mail recipients separated by comma.
            -h: This help message.
            -v: Revision number of this script.

If you run the script on Linux and you are lacking the ksh executable then you are faced with the following error message:

#-> /home/gdhaese1/bin/fix-TLS-Logjam-vulnerability.sh
-bash: /home/gdhaese1/bin/fix-TLS-Logjam-vulnerability.sh: /usr/bin/ksh: bad interpreter: Too many levels of symbolic links

However, you can easily use the bash shell instead as you can see below:

#-> bash /home/gdhaese1/bin/fix-TLS-Logjam-vulnerability.sh
-----------------------------------------------------------------------------------------------
                   Script: fix-TLS-Logjam-vulnerability.sh
       Executing User: root
     Mail Destination:
                 Date: Fri Sep 11 08:32:04 EDT 2015
                  Log: /var/tmp/fix-TLS-Logjam-vulnerability.log
-----------------------------------------------------------------------------------------------

  -> Collect all httpd related configuration files...
  -> Search http configuration files containing SSLCipherSuite keyword

  -> Search for +EXP vulnerability with TLS
  -> None of the httpd related configuration files are vulnerable.

Here, you can see the script in action to fix some hhtpd configuration files:

#-> /home/gdhaese1/bin/fix-TLS-Logjam-vulnerability.sh
-----------------------------------------------------------------------------------------------
               Script: fix-TLS-Logjam-vulnerability.sh
       Executing User: root
     Mail Destination:
                 Date: Fri Sep 11 08:39:41 EDT 2015
                  Log: /var/tmp/fix-TLS-Logjam-vulnerability.log
-----------------------------------------------------------------------------------------------

  -> Collect all httpd related configuration files...
  -> Search http configuration files containing SSLCipherSuite keyword

  -> Search for +EXP vulnerability with TLS
  -> Configuration file /opt/hp/hpsmh/conf/extra/httpd-ssl.conf is vulnerable for OpenSSL Logjam
  -> Configuration file /opt/hp/hpsmh/conf/original/extra/httpd-ssl.conf is vulnerable for OpenSSL Logjam
  -> Configuration file /opt/NAI/LinuxShield/apache/conf/httpd.conf is "not" vulnerable for OpenSSL Logjam

  -> Make a backup copy of httpd configuration files
  -> Backup file /opt/hp/hpsmh/conf/extra/httpd-ssl.conf.2015-09-11 created
  -> Backup file /opt/hp/hpsmh/conf/original/extra/httpd-ssl.conf.2015-09-11 created
  -> Disable EXP in httpd configuration files
  -> Fix /opt/hp/hpsmh/conf/extra/httpd-ssl.conf
SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL
  -> Fix /opt/hp/hpsmh/conf/original/extra/httpd-ssl.conf
SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL
  -> Evidence of disabled EXP flag in /opt/hp/hpsmh/conf/extra/httpd-ssl.conf
SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:!EXP:+eNULL

  -> Evidence of disabled EXP flag in /opt/hp/hpsmh/conf/original/extra/httpd-ssl.conf
SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:!EXP:+eNULL

  -> Restarting httpd daemons...

Stopping hpsmhd:                                           [  OK  ]
Starting hpsmhd:                                           [  OK  ]
Stopping httpd:                                            [FAILED]
Starting httpd:                                            [  OK  ]
/opt/NAI/LinuxShield//apache/bin/apachectl restart: nailswebd not running, trying to start
no listening sockets available, shutting down
AH00015: Unable to open logs
/opt/NAI/LinuxShield//apache/bin/apachectl restart: nailswebd could not be started

-----------------------------------------------------------------------------------------------
Finished.
-----------------------------------------------------------------------------------------------

And, below, the script finds no httpd configuration files which are vulnerable:

#-> /home/gdhaese1/bin/fix-TLS-Logjam-vulnerability.sh
-----------------------------------------------------------------------------------------------
               Script: fix-TLS-Logjam-vulnerability.sh
       Executing User: root
     Mail Destination:
                 Date: Fri Sep 11 08:47:16 EDT 2015
                  Log: /var/tmp/fix-TLS-Logjam-vulnerability.log
-----------------------------------------------------------------------------------------------

  -> Collect all httpd related configuration files...
  -> Search http configuration files containing SSLCipherSuite keyword

  -> Search for +EXP vulnerability with TLS
  -> Configuration file /opt/NAI/LinuxShield/apache/conf/httpd.conf is "not" vulnerable for OpenSSL Logjam
  -> Configuration file /opt/hp/hpsmh/conf/original/extra/httpd-ssl.conf is "not" vulnerable for OpenSSL Logjam
  -> Configuration file /opt/hp/hpsmh/conf/extra/httpd-ssl.conf is "not" vulnerable for OpenSSL Logjam

  -> Make a backup copy of httpd configuration files
  -> Disable EXP in httpd configuration files
  -> Restarting httpd daemons...

-----------------------------------------------------------------------------------------------
Finished.
-----------------------------------------------------------------------------------------------

We hope you might find the script useful! Gratien

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