The iText 7 Core 7.1.18 release is a maintenance release for iText 7.1.x which includes some recent CVE mitigations and backports from 7.2.x releases.
It addresses two CVE issues (CVE-2022-24196, CVE-2022-24197) which were fixed in the release of iText 7 Core 7.2.2. In addition, we've also backported a fix from our 7.2.1 release which fixes improper nesting of canvas operators when converting SVG to PDF by supporting q/Q Operators inside BT/ET text blocks and objects.