Category Archives: infosec

infosec linux sysadmin technical

Scanning and Reporting on SSL Cert Expiry Dates – an SSL Certificate Scanner using bash, php and jQuery

A while ago I cooked up a bash script to scan relevant internal subnets for ssl certs, save/parse a copy of the x509 data and list all the discovered info in a delimited text file for analysis in a spreadsheet.

This works well by itself, but for the convenience of quick lookups without involving excel or libreoffice, a web page can be useful. PHP provides a simple method for converting a delimited file into a table (fgetcsv() ), and jQuery has a great plugin called tablesorter which allows you to do some quick sorting and filtering right there in the browser. It didnt take long to mash these together into a one script web page to display the sortable certificate data at a glance.

Sample screenshot:

Screenshot sample of scancerts

The sample only shows the three dummy values I’ve included in the demo, but I’ve used this in production with 600+ scanned certs and it works well.

Scancerts has two main components:

  1. Bash script which eats a text file containing a list of networks to scan, uses openssl, sed, awk, grep, cut, etc to generate another text file containing a delimited list of discovered certs.
  2. PHP script which turns the delimited text file into a HTML table, and augments it with some jQuery so your browser can sort and filter the HTML table on the fly.

Installation Steps

  1. Create a web-accessible folder on your linux box
  2. Unpack the files in the provided archive to the web folder
  3. Make sure file/folder permissions are set correctly (and you can run PHP!)
  4. Add the subnets you want to scan into ‘subnets.txt’
  5. Make ‘scancerts’ executable
  6. Run scancerts and optionally add it to cron
  7. View a nice sortable html list of discovered certs

Download: scancerts_v0.1.tar.gz

infosec linux sysadmin technical

Simple BASH script to mass query reverse DNS PTR records for a subnet

Wrote this up the other day to do a quick reverse PTR query of some internal subnets. Possibly handy if you don’t have quick access to another tool like dnsrecon.


#Populate subnets.txt with the first three sections of the target subnet IP, one subnet per line eg

subnets=$(cat './subnets.txt');
for subnet in $subnets
        for ip in $subnet.{1..255}
            dig -x $ip | sed -n '/ANSWER SECTION:/,/Query time:/p' | sed '/ANSWER SECTION/d' | sed '/Query time:/d' | sed '/./!d'
#echo $ip


I’ve since found the useful python based dnsrecon which seems to work really well for this also:

./ -t rvl -r