A security issue has been discovered that we consider to be of a high severity, and as a result we have decided there is a need to release an immediate patch for it.
Although not related to the new release, it is unfortunate timing so soon after the release, but we take security very seriously and so if an issue becomes apparent to us, we will always issue a patch immediately for it as our track record with patches in recent years demonstrates.
Applying the patch is very simple. It's just a single file to update. There are separate versions of the file for each release of WHMCS from V4.0 up to the very latest V5.0 release. The patch download consists of a single file which just needs to be unzipped, and then uploaded to the /includes/ folder replacing the existing file. Download links are as follows:
