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Category Archives: Security

Windows: What do I want to see as default browser

Windows: What do I want to see as default browser 1

Why Did I bother with it at all?

As I wrote before it is more convenient and secure to have something small, fast and feature limited as your default browser (valid decision for all OSes out there).
Well times go by and nice small Qtweb got outdated with development on it stopped about 6 years ago and new standards (namely SSL/TLS) and new vulnerabilities came out, so I decided
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Sysadmin: Letsencrypt renewal htaccess redirect bypass

With increasing role of HTTPS websites (Google pushing everybody to run only HTTPS websites considering regular HTTP as insecure) the service provided by Let’s encrypt becomes critically important. But there is a catch – once you get the certificate and redirect your site to HTTPS using .htaccess you will get a problem renewing certificate because 301 redirect breaks the challenge verification and the command

gives an error about authorization problem.
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Sysadmin: Virtualmin and Letsencrypt integration

Sysadmin: Virtualmin and Letsencrypt integration 2Sysadmin: Virtualmin and Letsencrypt integration 3
If you are using webmin excellent system for managing virtual host configuration it would make perfect sense to integrate with it the popular certificate authority Letsencrypt that issues completely free SSL certificates.
There are few initial steps that has to be made nside Webmin in order to make it utilize Letsencrypt SSL certificate issuing process for configured virtual hosts. I have successufully configured and used Webmin version 1.831 and certbot-auto 0.12. YMMV.
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Sysadmin: How to install Letsencrypt on CentOS

Sysadmin:  How to install Letsencrypt on CentOS 4
Since Letsencrypt started their services life became much easier (or less). You can get free valid and secure SSL certificates that are recognized by majority of browsers, but for that you need to do some initial configuration and keep in mind that if you don’t renew all these nice certificates will turn into pumpkin after 2 month.
Here is the one liner command to install certbot-auto in CentOS 6 (requires additional Python 2.7 from EPEL repo)

Almost, the same for the CentOS 7 just without Python.

Here is how quickly request/retrieve certificate for your website on domain.com that is hosted under /home/domain/public_html from command line (presuming that the site is answering on this server already e.g. DNS and web server configured properly)

If the request was successful your new certificates could be accessible from /etc/letsencrypt/live/domain.com, where
privkey.pem – is the certificate key, cert.pem – bare certificate fullchain.pem – certificate along with the whole CA chain.
Don’t forget that these are valid for 2 month only. You’ll need to run

after that to get valid certificates.

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SSL protocol error 525 for nginx solved

SSL protocol error 525 for nginx solved 5
I’ve hit an unusual error the other day – I had to configure couple of SSL virtual hosts on Nginx web server. I didn’t expect to see any problems with that – it’s really simple and very well documented. The purpose was to switch Cloudflare CDN crypto option from “Flexible” to “Full”, to avoid unencrypted connection between Cloudflare and the server itself. The tricky part is that you have to have SSL virtual host configured on the server side before doing redirection otherwise you will get redirect loop.
I configured both of the SSL virtual hosts (thought second virtual host with ssl_certificate and ssl_certificate_key commented out) and tried to modify Cloudflare configuration – and then I’ve got 525 protocol error. I turned off the caching and tried to investigate.
SSL protocol error 525 for nginx solved 6

I tried to use OpenSSL to troubleshoot SSL connection with “s_client” option, trying to connect to each SSL virtual host directly, bypassing Cloudflare and I saw an interesting picture

and more verbosely

And then it hit me – I’ve turned on SSL mode on the virtual host and not specified nor certificate no key, then I’ve configured another SSL virtual host with valid certificate and key configured but the SSL is running on the single IP so it’s in SNI mode, sends me an EMPTY SSL SNI negotiation start. In order to avoid the problem I need to have valid certificates for ALL my SNI SSL virtual hosts. After I altered my configuration the problem was fixed.

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Centos: How to fine tune your Apache SSL server

Centos: How to fine tune your Apache SSL server 7
The fine tuning of the SSL server side configuration is slow and tedious but necessary procedure. It’s always good to have your SSL site to conform the most latest security standards. It boosts ego and makes customer happy too. It turns out that all you need for that is already at your disposal the point is to properly configure it.
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Sysadmin: Brute force detection – custom rule for SMTP and SSH

I wrote before about excellent tool BFD that allows to block brute force password guessing attempts on different network services.
I prefer it to Fail2ban because of portability (bash script) system resource consumption (bash script!) and extendĐ°bility (true “unix way” modularity).
I also wrote before a brief instruction on how to extend BFD with your own rule to fight with apache/Wordpress DOS attack.
In this post I will show you how to write custom rules to block SMTP password guessing brute force attempts and SSSHD

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Windows: Set lightweight web browser as MS windows default web browser application.

qtwebI was thinking the other day – it’s not really safe to have MS windows default browser set to MS Internet Explorer, so any URL you accidentally click will be open with it. For the work related activity I user portable browsers. But what about everything else – this is not really safe no matter how many MS security updates are published every week.
So, I decided to find something really small and “feature-poor” to assign it to the default browser.
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Sysadmin: How to see the name of PHP script that sent that e-mail

phplogo SPAM e-mail is the common problem these days and in most cases the cause of this problem is the lack of security on the hosted web sites. Various badly designed PHP scripts expose the hosting server MTA to be used as SPAM e-mails source. First and foremost step in resolving this problem would be to determine the originating PHP script that was used to send e-mails.
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Sysadmin: “[warn-phpd] mmap cache can’t open file … ” mystery solved

Sysadmin: "[warn-phpd] mmap cache can't open file ... " mystery solved 8
Yesterday I was asked by one of our old customers to help solving very interesting problem – he put some php files outside of apache DocumentRoot on his server and the apache could not access the files, producing very interesting lines into apache default error_log

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