Mojolicious::Plugin::CaptchaPNG version 1.05 for Perl uses a weak random number source for generating the captcha. That version uses the built-in rand() function for generating the captcha text as well as image noise, which is insecure.

• https://metacpan.org/release/GRYPHON/Mojolicious-Plugin-CaptchaPNG-1.04/diff/GRYPHON/Mojolicious-Plugin-CaptchaPNG-1.05/lib/Mojolicious/Plugin/CaptchaPNG.pm
• https://metacpan.org/release/GRYPHON/Mojolicious-Plugin-CaptchaPNG-1.06/changes
• https://metacpan.org/pod/perlfunc#rand
• https://security.metacpan.org/docs/guides/random-data-for-security.html