What would cause PHP variables to be rewritten by the server?

Question

I was given a VM at my company to install web software on. But I came across a rather bizarre issue where PHP variables would be overwritten (rewritten) by the server if they ma

Answer 1

Output overwriting is possible within Apache by using mod_perl: PerlOutputFilterHandler.

The following could be added to an apache.conf to set the output filter:

    PerlSetVar Filter On
    PerlHandler MyApache2::FilterDomain
    PerlOutputFilterHandler MyApache2::FilterDomain

Example filter handler code:

#file:MyApache2/FilterDomain.pm
#--------------------------------
package MyApache2::FilterDomain;

use strict;
use warnings;

use Apache2::Filter();
use Apache2::RequestRec();
use APR::Table();

use Apache2::Const -compile => qw(OK);

use constant BUFF_LEN => 1024;

sub handler {
    my $f = shift;
    my @hostname = split(/\./, $f->r->hostname);
    my $new_hostname = $hostname[0].".".$hostname[1];

    unless ($f->ctx) {
        $f->r->headers_out->unset('Content-Length');
        $f->ctx(1);
    }

    while ($f->read(my $buffer, BUFF_LEN)) {
        $buffer =~ s/([a-z0-9]+)+\.domain\./$new_hostname\.$1.domain\./g;   
        $f->print($buffer);
    }

    return Apache2::Const::OK;
}
1;

More on Apache mod_perl filters can be found here: mod_perl: Input and Output Filters