Category Archives: Uncategorized

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Squid Nuggets Introduction

About me

My name is Eliezer Croitoru and I’m a Linux and Database systems administrator for the past 14 years. I have been a member of the Squid-Cache Users and Developers community for many year.

My contributions to the Squid-Cache community includes the StoreID feature, free users support on the mailing list and the unofficial public Enterprise Linux  distributions (CentOS, Oracle, Fedora, Rocky and Alma) RPM’s repository.

I have also developed a bunch of Squid external acl helpers and utilities over the years for many purposes and orginizations. One of the most well known projects I have assisted with is with mentoring  BGU students for the IEEE publication “Website Fingerprinting Through the Cache Occupancy Channel and its Real World Practicality“.

local Mirror: RobustFingerprinting-TDSC

So what are these nuggets about?

Squid is a very complex piece of software and in it’s code embedded a lot of wisdom and effort which is there since 1985 and years back.

Over the years Squid was converted from C to C++ and a lot of helpers were written in many different programming and scripting languages. Each and every tiny piece of concept and idea when written in C or C++ is somehow going to require digging and archeological staff and work to understand and maybe re-design in the far future ( if at all). On my research of the Squid project over the years I learned a lot of things which I believe can be summarized for programmers, admins and engineers. For IT specialists the project can be an art show which they can observe and enjoy from the beauty of Computer Science.

Specifically I wanted to take Squid ACLs and SquidGuard internals and drill into them demonstrating with code (mainly using pesudo and ruby)  how their algorithms and implementations  can be re-written in modern languages.

I remember that a developer told me in the past the next sentence: “If you write it in perl it will work forever.” and it’s something which can be said on many higher level languages compared to much lower level languages. This with the AI platforms improvements in the couple years there is a possibility that many tools can be re-written much easily to achieve similar goals with less effort then in the past.

So the goal is to take piece of Squid and SquidGuard and share them as tasteful nugget snacks .

What is a Proxy Server and specifically HTTP proxy server?

Technically speaking a proxy server is a server that does a task for the client which is either the actual user or an organizational unit.

It can be a home, office, ISP or in much larger scales governments. And in this series I will focus on ACLs enforcement using Squid and other programs which Squid can delegate some aspects of the ACLs to them.

 

Prerequisites

To understand some of the content you are required to know some basics on “how the internet works” such as IP with it’s 7 layers and specific protocols such as DNS, HTTP and TLS. You need to also have the basic knowledge on how to use basic tools such as telnet or netcat and openssl or any other UI based equivalent.

Apart from that you must know some basic concepts of programming CLI( STDIN/STDOUT) based tools. If you know network programming then I hope it will be fun for you.

There are also couple concepts in Databases and Data Structures which are required so you would be able to appreciate the greatness of some of the simplest things which are embedded inside Squid and SquidGuard.

Some Additional resources

 

 

 

https://cs50.harvard.edu/x/2019/notes/5/

 

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Windows 10 Default Group Policy Restore

Based on the article at the bottom I am adding to my Journal a nice way to restore Windows 10 Pro to My Default Group Policy rules.

Recipe:

  • Download the GroupPolicy.7z  file
  • Backup your current system group policy folder:
    %systemroot%\System32\GroupPolicy
    Into a zip\tar\7z\other.
  • Delete all files in your destination system Group Policy folder:
    %systemroot%\System32\GroupPolicy\
  • Then extract the GroupPolicy.7z file content into the Group Policy folder:
    %systemroot%\System32\GroupPolicy
  • Start a command line(cmd) in administrative mode and run the command:
    gpupdate /force
    or restart/rebot your PC.

This helps to resolve some issues related to latest Microsoft Windows 10 Updates release.

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DNS as an API

I am happy to “Certify” Squid-Cache version 3.5.19 as
“Works For Me” on
CentOS(6+7), SLES(12SP1), Oracle Linux(6+7), RHEL(7), OpenSUSE(42.1 Leap), Debian(8.4), Ubuntu(14.04+16.04)

HTTP is commonly used as an API for many purposes in any industry and in many cases if you analyze an API specs and output you can see that some thinking was invested in it.

Around the Internet we can find many ideas about API’s and while some are well published others are long forgotten and are considered “old”. It is true that when you look at some of the API’s they might look “cryptic” or “malformed” but these have a purpose. Most of these APIs was meant to be public and as users we have access to all of them. But also many API’s requires some level of authentication or authorization which was clearly meant to not be fully public.

Some hackers around the world see the opportunity to “hack” something  when possible. From my own API’s which includes: HTTP, SMTP, DNS, WIFI HotSpot, Moblie and many others it is clear that some might think that it’s funny to send some malformed packets towards a Router or an AP. But I feel that there is a need to clear couple things out for any hacker.

Behind any System on the Internet there is some person which deserves respect. The fact that the API is there means that you are not allowed to hack it by it’s owner unless it was designed for it.
When comparing the real world to the Internet API’s not anyone can enter any door or any place. Not anyone can enter a closed party or a secured area. It would be a bit different since the minimum requirements to enter one place would not be the same for another.
For example, in the hackers world it’s known that there are ways to prove your value and earn your “nick” or “name”. Some hacking cultures are restrictive in their approach and respect any API avoiding the flame of war. While others think it’s better to hack some API as a Proof Of Concept or a Proof Of Knowledge.

White? Black? Green? Red? is there any meaning to all of these?
My answer is that all of these are hats, I do not have one and I do not want one. I am a simple person who has couple very simple API’s under his hands. But I learned that to give a good example is a profession. Specifically it’s not simple to give an example for a hacking kid. If any hacking kid wants to hack something, like in the real world, there are playgrounds for this sole purpose and an example would be canyouhack.it. Also these days if you want to learn how things work in the micro level we have Lots of free and open Virtualization platforms. These exist in any part of the Industry from the electricity level to the application.
All these tools was meant for the sole purpose of allowing the learning curve to be easy simple and safe, to use a real world power tool in an environment which will tolerate things which might not be acceptable in the real world API’s.

Not too far from the invention of HTTP the DNS system was invented and it’s an API like HTTP and many others. It is commonly used over UDP and has a very limited size and format but it has power in the same level as a button on a car dashboard. Technically it can and is being used in many places as a trigger to some system. Indeed UDP is not reliable at the same level of TCP but when the network equipment is trusted then there would be no reason to not use UDP.

A list of things that can be done using a DNS service messaging:

  • On\Off electrical switch
  • Identity signaling(AKA Port Knocking)
  • Banking transactions
  • Queue status updates
  • Alerts Signalling

And many other uses which can give an example to what an API can look like. I had the pleasure to read couple books about APIs published by Nordic APIs which gave me a fresh perspective on how others see an API and what might happen on the wild Internet that requires attention.

One key point which I learned from them is mentioned in the video “Good APIs aren´t built in a day”

And links to books from Nordic APIs  which I had the pleasure to read:

eBook Released: Securing the API Stronghold

API Security: The 4 Defenses of The API Stronghold

  • “Works For Me” means that it was tested on a testing environment under real world usage in a forward proxy mode with daily usage traffic such as Browsing News, Video, Learning and Games sites. Special applications that was tested are SKYPE, IRC and couple other applications inside a fully trusted network.
  • An Advice: Any system which sits against a non-trusted and a hostile public or private network should be “Harden” both in the squid configuration level and other lower levels.
  • This specific version(3.5.19) was tested also on Intercept proxy mode and ssl-bump but only on forward-proxy and not Intercept mode.
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A Proxy for each Internet user! The future!

What a proxy is as a tool? is it a war or a life assisting tool?

The Internet is a reflection of the real world, and the world in general can at times be a war-zone but is more of a heaven. A proxy basically is an assisting tool to the warrior of Internet. We can give it a shape of a Squid or of a Katana, but the tool by itself is there to help. And despite to the fact that in the science fiction and fantasy world the image of such a tool might be one, the truth is that it can take multiple forms. Also not every Internet warrior needs the same tools as another. Some needs raw Internet while others needs a more digested one, based on the age and experience.

Compared to the first human which god have created, we are engaging the world in a much higher level then raw basic input and output. And since we are at about the 6k year since this world creation, we have an embedded proxy in each and one of us. Every pair of parents shares with the kids some amount of tools. Yes this tool of war which helps us to digest raw Internet Input and Output.
A wise man once told me “Your tongue  has lots of power, do not do harm!” and I was wondering to myself couple years about this fact.
I knew that we have power in our words but compared to the raw hardware we are in a much higher level. We all have a proxy embedded inside of us and this is a fact. Now the question which stands in-front of  every Internet user and admin is whether he wants to utilize this tool as an assisting glass to the lower levels of the Internet and build the next and higher level, or to harm what is already there.

Little by little in life we discover our proxy powers and we can choose to either take these into our hands and to do good, or to use these powers in a way that will shame our form as a creation of a much better world. Yes, despite to what many non-experienced kids say we have a a very good foundation but we need to maintain it.

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Squid 3.5.15+16 release article

I am happy to release the article for the new squid 3.5.15+16
Until now the release was for the RPMs but I hope that from now on it will be much simpler to release every RPM.

The Fantasy Of Packaging
( A response to: Slamming Your Head Into Keyboard)

I was asked couple times “Why do you package?” and the simple answer is that I need it. But I must admit that it’s not because other developers and packagers doesn’t do a great job.
It’s just that I have couple specific systems that I operate and I need them to be up to date and until now I didn’t got the option to have someone that will take enough on his shoulders to make it happen in an Enterprise level.
And of-course it’s not that they do not want to, but since any Enterprise level distribution gives a good foundation for a very complex systems. When they develop and package they test and test and many other things until they can Insure themselves  and their clients.
It’s as simple as this. If in some case you have found an issue, they should help you with it by the level of contract you have with them.
For example since I have a Windows licensed PC and a licensed SLED Laptop I expect them to release at-least security updates.

I know that every major Linux Distribution does it’s job in a very good way. I know it since I can see their src.rpm packages and compare between my work to them.
Basically if you are a young man or a kid, the example from the scene at Toy Story which handy is opening the presents packages at the party and then he finds “Buzz light year” in a big box would describe to some how handling a package shouldn’t happen in the Enterprise level businesses.

(from about 09:00 to 14:00 minutes in the movie)

An admin should rely on the packages and packagers in general but he needs to plan and understand the nature of the update in order to anticipate what could be done in the update of the system.
If you have a big system which clients are using you cannot just run “yum update xzy” because you want to update. And specifically with squid you need a strategy that will allow you to sort of “bypass” this specific server and use another server in the mean while.
On small scale it’s simply adding another of squid instance on the same machine or to access squid using a haproxy LB.

It’s not really requires magic just basic skill knowledge and responsibility, if you are lacking one of these you should invest some time to acquire theses skills.

If for some reason for your or others business the generic packaging  doesn’t fit then you should understand that their aim was not you exactly but to another audience. And yes… it’s hard to see a package that does weird things like giving suid (chmod u+s XYX) to a file which actually is just a tiny script which should never run under root. But these things happens when the packager is novice enough to not understand they meaning of the work.

RPMs Automation: Here I come!!!

The squid-cache project and many others do not Package things in binary format and it’s important to understand that every Open-Source project probably have limited resources and goals and squid-cache is probably one of them.
All the sys-admins that uses my RPMs will probably enjoy them for a very long time but I have started to move from the manual hard labor RPMs creation to an automated one.
It means: That the packages will be pushed to the repository automatically for any squid release. My plan is to “certify” each of the RPMs or a release by a set of tests which are mainly manual rather then automated.
I haven’t decided yet what to do when a release fixed one bug but made another one but I will probably bump the RPMs version after basic testing.

And I would like to dedicate this amazing remix for all the amazing young IT industry mages that works many nights to give the Magical Internet be has great as it is now.

—www.youtube.com/watch?v=YFwoigs7Lhk
The above link was removed so another copy:

All The Bests,
Eliezer Croitoru