PERL

Released in 1987, PERL has a long history of changes and revisions.   In 1998, it was also referred to as the "duct tape that holds the Internet together" in reference to both its ubiquitous use as a glue language and its perceived inelegance 
(https://en.wikipedia.org/wiki/Perl#:~:text=Perl%20was%20developed%20by%20Larry,evolved%20into%20a%20separate%20language).

With respect to server-side usage by websites Perl has declined over the years from 1% to 0.1%
https://w3techs.com/technologies/history_overview/programming_language/ms/y

Using Cybersecurity controls to block access to online resources based upon Categorisation, Deny Lists, Firewall rules etc is not effective as Data Loss Prevention technologies.
The use of this upload method demonstrates it is trivial for anyone that has access to a web browser and the internet, to easily move sensitive/confidential data outside of organisations.

The likelihood of such a Data Loss risk event occurring must be considered.
The impact of a Data Loss risk event will depend on the content and amount of information that has been uploaded via PERL.

Use DLP-TEST to assess: - 

- Coverage of DLP Technologies to detect data being uploaded via the PERL method.
- Capability of DLP Technologies to accurately detect sensitive/confidential data being uploaded via the PERL method.
- Ability of DLP technologies to ignore data being uploaded that is NOT sensitive or confidential.