4 Nisan 2020 Cumartesi

How to automate enumerating base64 encoded parameter to exploit IDOR using python

In this article i want to show you how easy to automate an exploitation of an IDOR vulnerability using Python requests framework, where the IDOR parameter is base64 encoded.

If the parameter is not encoded with base64 you can use Burp intruder tab to create payloads and test the IDOR vulnerability.

First we should find the IDOR parameter to enumerate. Assume that you have the following url that you can download a report.

http://www.example.com/Download.ashx?RprtTkn=MTExMjIyfGZpeHBhcmFtZXRlcnxhbm90aGVyX2ZpeGVkX3BhcmFtZXRlcnw==
Look at the token carefully and try to base64 decode it. Keep in mind wherever and whenever you see such a string first try to base64 decode. You can use Burp decoder  tab or any other online tool to decode . After decoding the base64 encoded string we get the following decoded string
111222|fixparameter|another_fixed_parameter|
We are not interested with the fixed parameters So let's focus on the first bold part of the string where we can enumerate and find out whether it is exploitable or not.

To do this ;

  1. We should start a loop to change the bold part of the string which will be our IDOR enumeration value
  2. Then construct and base64 encode  
  3. Then send the request
Before starting to write our python code you can easily copy the authenticated request as cURL from chrome and convert it to python requests code using an online service . Because you will need to add authentication cookie and other headers before you made a request to the url. 

Combining all of the above explanations we have the following python code to enumerate the parameter.  








22 Aralık 2019 Pazar

Solving Palo Alto User-IP Mapping issue while connecting via Pulse Secure VPN

     In Palo Alto firewalls you can create username based rules. But TCP connections do not rely on usernames, they are based on source ip address, destination ip address, source port, destination port etc. So there should be mapping that will tell firewall which ip is mapped to the username. Palo Alto has various methods to collect and populate user-ip mappings table.
   
     In a Windows environment firewall admins used to integrate User-ID agent with Active Directory to listen logon events. So when a user logins to his/her PC in a domain, user-ip mapping is created from the logon event that is generated on the DC.

    After this brief introduction about user-ip mapping lets come to the issue, If  two users get same ip in a sequence.

   When users get connected to the corporate network via Pulse Secure VPN they are assigned an ip from the pool of a DHCP server. After this assignment, Palo Alto user id agent creates the user-ip mapping. When that specific user disconnected from the VPN, Pulse Secure sends DHCP release and the IP address sent back to the available ip pool. But the user-ip mapping is not cleared on the user-id agent side. So when another user gets connected and gets the same ip, all rules will be also valid for this user. But this is a really serious security issue.

   To solve this issue you can configure user-id agent as a syslog server and configure Pulse Secure VPN to forward auth events to this server. ,

   First you should define login-event regex to create user-ip mapping and logout regex  to clear user-ip mapping.





     Then you should add Pulse Secure VPN ip as a syslog sender and add above event filters to the profile.



    After these settings user-ip mappings will updated as expected. And no wrong user-ip mapping will occur.



21 Haziran 2018 Perşembe

Zimbra Visual Log Analysis with ELK Stack

For log analysis ELK(ElasticSearch-LogStash-Kibana) stack  is a powerful tool for Zimbra Mail Server logs, you can search logs and easliy create visually appealing graphics with Kibana interface.

In this post we will analyze the logs to find out which ip addresses abusing logins or brute forcing to Zimbra mail server.

So we first assume that if a single ip interacts with at least 5 different accounts we will count it as malicious usage. You should baseline your system accordingly otherwise there will be false positive decisions.

Now let's create the pie chart that will tell us these IP addresses visually



Then choose the following index



Now we will see whole number of logs to divide pie click Split Slices
Then
  1. Choose Terms as for the Aggregation 
  2. Choose src_ip for the Field
  3. Write top number of ip addresses you want to see in the Size section
Now you should see a pie chart as below.



Now we should add sub-bucket to see how many accounts these ip addresses interact.
So click Add sub-buckets, click  Split-Slices and configure the sub-bucket as below



Now you should see the following pie chart where the inner slices shows the source ip addresses and outer slices shows usernames that individual ip addresses interact.


Now lets describe what the pie chart tells us.

If you see an  inner slice sweeping one outer slice in 1 day or 1 hour period that is we can safely assume that this is not a malicious ip address.

But if you see an inner slice sweeping more than 5 outer slice than we can conclude that there is a malicious activity either brute force or logged in with multiple accounts from one ip addresses.




So to find out a brute-force we should add a filter with the string "invalid credentials".

19 Nisan 2018 Perşembe

Security Auditing with InSpec

InSpec is a tool from CHEF. With InSpec you can ,

  • Audit Policies
  • Check security requirements
  • Conduct compliance checks

InSpec can be installed on Linux, Mac or Windows. InSpec rules are written in ruby files.

I will give you some examples from the github repo about this amazing tool.



describe package('telnetd') do
  it { should_not be_installed }
end

describe inetd_conf do
  its("telnet") { should eq nil }
end


This rule will check the system against the installation of telnet and disallow this insecure service.

To run inspec save the above code snippet to a test.rb fie and in the command prompt run the following command to conduct the test.


inspec exec test.rb
you can also test this requirements against to remote systems.

on your linux servers using ssh ,

inspec exec test.rb -t ssh://user@hostname

or on windows through WinRM

inspec exec test.rb -t winrm://Administrator@windowshost --password 'your-password'

if you are familiar with CHEF compliance check, you can also make compliance check with the following syntax


  inspec compliance SUBCOMMAND ...   # Chef Compliance commands



For example this code uses the sshd_config resource to ensure that only enterprise-compliant ciphers are used for SSH servers.

describe sshd_config do
  its('Ciphers') { should cmp('chacha20-poly1305@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr') }
end

You can see detailed tutorials in the following link 





13 Nisan 2018 Cuma

Moodle Quiz Activity with 500 Concurrent User

We have experienced a Quiz Activity with 500 concurrent user and i want share this experience with you. Because these insights are really valuable for system administrators, that i could not find any suggestion before this Quiz Activity.  Let me write the details about the system and the quiz activity.
We have installed moodle on a virtual machine VMWare with the following configuration.

We set the vm cpu to 16 shared vcpu,  and 24GB shared RAM
Running Centos 7.0 Minimal with php5.X, apache and mariadb with 700 max_connection setting.
Quiz activity with 20 Question and 30 Minute timespan and 17 Minute attempt time limit. 2 Question per page. Question order and choices were shuffled. Auto submit open attempt setting was on.




CPU and RAM usage was crucial for us. We see maximum 12 GB ram usage which is roughly 1 GB per 50 User
We see %95 CPU usage when the quiz started.

Before quiz started i stopped cron jobs and automated course backups.


3 Nisan 2017 Pazartesi

Email to user when a role is assigned

When an admin/teacher assigns a role to a user in course or category context you can send an email to the user which the role has been assigned by modifying the following moodle lib file.

/var/www/html/moodle/admin/roles/assign.php

In the file around the lines 103-111 by adding email_to_user() moodle lib function you can send the email to the user from the moodle support user. Be careful that email_to_user() function accepts from and to users as moodle user objects so you can not write simply emails and send.         

   foreach ($userstoassign as $adduser) {
                $allow = true;
 

                if ($allow) {
   
                    role_assign($roleid, $adduser->id, $context->id);


                    email_to_user($adduser, $supportuser, "Your role has been assigned in Moodle", "You have been assigned as a ".$assignableroles[$roleid]." in the ".$contextname ); 
                }
            }


After you add this the user will receive an email with subject "Your role has been assigned in Moodle" and message ie. "You have been assigned as a Course creator in the Category: Mathematics"

21 Şubat 2017 Salı

Ansible And Vmware

Do you know that you can manage your VMWARE virtual infrastructure with ansible. If you are a devops admin you can also use vRealize Orchestrator to provision test, product or beta stage servers for your developers. But if you do not need such an enterprise solution you also use Ansible to manage your vMWare infrastructure. As stated in Ansible web page you can use ansible for

  • Managing vSphere datacenters, clusters, hosts and guests
  • VM template and snapshot management
  • vSwitches, DNS settings, firewall rules and NAT gateway rules 
You can find the modules for vmware in the following link.

http://docs.ansible.com/ansible/list_of_cloud_modules.html#vmware

To be able to run vm modules you have the install the following python libraries.

pysphere
PyVmomi



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