Broken email sending with attachment due to malfucntioning base64 validation (catastrophic backtracking of regexp)

[pgolofit]

This line:

brevo-php/lib/Model/SendSmtpEmailAttachment.php

Line 267 in be204da

if (!is_null($content) && (!preg_match("/^(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?$/", $content))) {

Was Added around 4 months ago and broke email sending with attachments in this commit: 563eef8

Pattern /^(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?$/ works only for shorter strings up to 98288 characters. After that limit it fails and preg_match returns false. Which makes this setContent function to fail to recognise the correct base64 string.

This is due to catastrophic backtracking of regexp. More on this issue eg. here: https://medium.com/@catcatduatiga/when-regex-eats-the-cpu-a-postmortem-of-catastrophic-backtracking-in-php-and-how-tiny-patterns-can-64b2aa64a530

Because of this issue, only quite small attachments can be sent.

This can be fixed eg. with replacing the validation to base64_encode and base64_decode and comparison with oryginal string.

Temporary solution we found ist to switch off PRCE JIT temporaily ini_set("pcre.jit", "0"); but it is only temporary.