Replace the first line of hacked php scripts

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If you’ve ever dealt with web servers that have sites running wordpress, you’ve probably dealt with hacked php scripts since pretty much any server running wordpress is going to have a hacked copy of wordpress at some point.  One of the most common things script kiddies do after finding a vulnerable copy of wordpress is to insert backdoor code on the first line; something that looks like this:

<?php if(!isset($GLOBALS["\x61\156\x75\156\x61"])) { $ua=strtolower($_SERVER["\x48\124\x54\120\x5f\125\

As long as you can find a unique pattern that you know would not occur in any legit place in the file, it’s easy to replace the first line using a command line perl script:

find . -type f -name \*.php -exec grep -rl 'isset($GLOBALS' {} \; |xargs -i -n 1 perl -pi -e "s/^.+isset\(\$GLOBALS.*$/\<\?php/g" {}

In this case, I knew the website in question had no legit use of ‘isset($GLOBALS’ in any of the uncompromised php code, so that was the pattern I searched for.  The matching files are piped to xargs to execute a command against each file, and the command is a perl pattern replacement where it replaces the entire first line of the file with <?php to put them back to how they were.

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One Reply to “Replace the first line of hacked php scripts”

  1. Pierre-Philippe Lessard

    Your command was not a success for me (find: `grep’ terminated by signal 13).

    Instead, I created a small bash script :


    #!/bin/bash

    filelist=$(find . -name \*.php)

    for x in $filelist
    do
    sed -i '/isset($GLOBALS/c\<?php' $x
    done

    Reply

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