https://helpx.adobe.com/security/products/magento/apsb23-50.html
The vulnerability with the highest CVSS score of 8.8 (CVE-2023-38218) states that it is an unauthenticated privilege escalation due to improper input validation.
If we look at the diff we see a number of security related changes. One of those changes is the following in Magento\Customer\Plugin\Webapi\Controller\Rest\ValidateCustomerData::validateInputData:
Get a more debugable error message when DOM validation fails in Magento.
Original Error Message
1 exception(s):
Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'arguments': This element is not expected.
Line: 1471
Magento 2.3.7 and 2.4.2 ship with composer v2 support out of the box but as far as I can see the only thing that needs to happen is to use some more modern versions of certain composer plugins which are used by certain dependencies of Magento.
This means we should be able to add composer v2 support to older Magento2 versions as well if we get a bit creative.
See below for diffs of the composer.json files you can apply to your projects, be sure to keep a mental note of these things, they will need to maintained by yourself in case newer versions of these modules are released. And if one day you update to Magento 2.3.7 or 2.4.2 or higher, you can remove these changes again.
This page lists what caches or directories you will need to clear to apply various types of changes. It is consolidated and adapted from the complete official documentation on directories and caches.
💁 If your development environment supports it, you are better off using Vinai's automatic cache cleaner. As of this writing, the primary reason why it might not work is if your code is hosted on a NFS share (common with Vagrant).
These set of scripts are for Magento 2. For Magento 1, see this Gist.
Bash scripting cheatsheet: https://github.com/dylanaraps/pure-bash-bible#loop-over-files-and-directories