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+====== Blocking SemrushBot ======
+SemrushBot is an annoying web crawler that has proven to completely disregard the robots policies as well as hammering webservers hard by recursively following all the links on a website without delay and outright ignoring any repeating ''403 Forbidden'' error messages.
+{{:wizardale.png?nolink | Oh no, not this shit again! }} Folklore claims that SemrushBot helps your site generate revenue from ads but the question is whether that revenue outweighs the money spent accommodating SemrushBot's rampant behaviour that yields a morbidly increased server load.
+===== IP Layer =====
+On the IP layer:
+<code bash>
+iptables -t mangle -A INPUT -p tcp --dport 80 -m string --string 'SemrushBot' -j DROP
+</code>
+Which is an awful solution to get rid of this pest without even hitting the application layer!
+===== Apache2 =====
+If are okay with your frontend being hammered by this total garbage, then the ''SemrushBot'' user agent can be blocked in Apache2.
+Enable the ''rewrite'' module:
+<code bash>
+a2enmod rewrite
+</code>
+and include in virtual hosts:
+<code apache2>
+       <IfModule mod_rewrite.c>
+                RewriteEngine on
+                RewriteCond %{HTTP_USER_AGENT} googlebot [NC,OR]
+                RewriteCond %{HTTP_USER_AGENT} sosospider [NC,OR]
+                RewriteCond %{HTTP_USER_AGENT} BaiduSpider [NC]
+                # Allow access to robots.txt and forbidden message
+                # at least 403 or else it will loop
+                RewriteCond %{REQUEST_URI} !^/robots\.txt$
+                RewriteCond %{REQUEST_URI} !^/403\.shtml$
+                RewriteRule ^.* - [F,L]
+       </IfModule>
+</code>
+which is a bad solution because ''Forbidden'' is meaningless to the greatness that is ''SemrushBot''.
+===== Varnish =====
+Perhaps blocking with Varnish may be a good compromise between having your Apache2 hammered and blocking the string ''SemrushBot'' on the IP layer:
+<code varnish>
+sub vcl_recv {
+    # Block user agents.
+    if (req.http.User-Agent ~ "SemrushBot") {
+        return (synth(403, "Forbidden"));
+    }
+    # ...
+}
+</code>
+An even better method would be to use fail2ban to block ''SemrushBot'' by reading Varnish logs on the frontend or Apache2 log files on the backend which will prevent either of them to get hammered with requests.
+===== Varnish and Fail2Ban =====
+For Varnish, copy ''/etc/fail2ban/filter.d/apache-badbots.conf'' to ''/etc/fail2ban/filter.d/varnish-badbots.conf'' thereby duplicating the Apache2 configuration (this works due to NCSA log format) and edit ''/etc/fail2ban/filter.d/varnish-badbots.conf'' to add ''SemrushBot'' to the list of custom bad bots:
+<code>
+badbotscustom = EmailCollector|WebEMailExtrac|TrackBack/1\.02|sogou music spider|SemrushBot
+</code>
+then correct the ''failregex'' line to:
+<code>
+failregex = ^<HOST> -.*(GET|POST|HEAD).*HTTP.*"(?:%(badbots)s|%(badbotscustom)s).*?$
+</code>
+and finally add the following to the jail configuration:
+<code>
+[varnish-badbots]
+enabled  = true
+port     = http,https
+filter   = varnish-badbots
+logpath  = /var/log/varnish/varnishncsa.log
+maxretry = 1
+</code>
+and restart ''fail2ban''.
+To check that the bots are being banned, tail ''/var/log/syslog'' and look for:
+<code>
+fail2ban.jail[18168]: INFO Jail 'varnish-badbots' started
+</code>
+indicating that the ''varnish-badbots'' jail has started.
+Hopefully followed by lines similar to:
+<code>
+NOTICE [varnish-badbots] Ban 46.229.168.68
+</code>
+====== Intercept SSL 2.0 / SSL 3.0 Using SSLsniff ======
+Redirect SMTPs to custom port for SSLsniff:
+<code bash>
+iptables -t nat -A PREROUTING -p tcp --destination-port 995 -j REDIRECT --to-ports 4995
+sslsniff -a -c /usr/share/sslsniff/certs/wildcard -s 4995 -w /dev/stdout
+</code>
+Example Session:
+<code>
+1385227016 INFO sslsniff : Added OCSP URL: ocsp.ipsca.com
+1385227016 INFO sslsniff : Certificate Ready: *
+sslsniff 0.8 by Moxie Marlinspike running...
+1385227031 DEBUG sslsniff : Read from Server (mail.net.hu) :
++OK POP3 PROXY server ready <7575E80698581E88C26B60701C2C67717034A020@smtp.mail.net.hu>
+1385227032 DEBUG sslsniff : Read from Client (mail.net.hu) :
+USER harry
+1385227032 DEBUG sslsniff : Read from Server (mail.net.hu) :
++OK Password required
+1385227032 DEBUG sslsniff : Read from Client (mail.net.hu) :
+PASS secretpassword
+</code>
+====== Normalizing the No-Login Shell after Debian Updates ======
+After successive updates and corrections, the password database might not get updated such that scanning ''/etc/passwd'' for users reveals multiple variants of the ''/usr/sbin/nologin'' shell such as:
+<code>
+systemd-coredump:x:998:998:systemd Core Dumper:/:/sbin/nologin
+rslsync:x:999:999::/home/rslsync:/sbin/nologin
+sshd:x:107:65534::/var/run/sshd:/usr/sbin/nologin
+</code>
+where the correct answer seems to be ''/usr/bin/nologin'' and as one might imagine, the other file paths do not even exist leaving an opportunity for an attacker to slide a shell into place.
+A solution to batch-change the shell for all users that have no-login shells, correcting the path, would be the following:
+<code bash>
+for i in `cat /etc/passwd | grep nologin | awk -F ':' '{ print $1 }' | xargs`; do usermod -s /usr/sbin/nologin "$i"; done
+</code>
+====== The Android Security Model is Just Liability Dumping ======
+{{fuss:fuss_security_android_liability_dumping.png?512}}
+As the title says, the Android "security model" has nothing to do with security and is just a liability dumping scheme with no value in regards to security or privacy. The same liability dumping scheme found in Android, is also implemented by platforms such as Facebook, and in spite of the fact that it is advertised as keeping users secure, it has no worth with regards to security.
+As the flowchart would imply, after downloading an application on Android, the application is a black-box with unknown capabilities that can carry out any actions it is programed to carry out. By asking the user whether they consent to various permissions to be granted, the user always takes the decision without any foreknowledge of what granting the permission would imply. In case the user denies a permission request, then, at best, the application becomes crippled, some features will not work and it and might develop some unexpected behavior at some later date (for example, in the middle of some activity, some file-transfer operation might not work, making the user wonder why), or at worst, the application will outright crash or refuse to work at all. Due to the former, the user will always take decisions, on say, arbitrary grounds: personal convictions, paranoia, guesstimates of trust, etc, when accepting or refusing the permission prompt for an application without any informed knowledge, nor any guarantee on how the application will be using the permission.
+On social media platforms, fine-grained permission controls are most of the time requested on an "all-or-nothing" basis, in the sense that the user is just presented a bulk list of permissions they would have to accept, for the application to work. If the user rejects the permission prompt, then the entire application does not work at all (which is even less than partial functionality on Android).