Integer wraparound in multiple PostgreSQL libpq client library functions allows an application input provider or network peer to cause libpq to undersize an allocation and write out-of-bounds by hundreds of megabytes.  This results in a segmentation fault for the application using libpq.  Versions before PostgreSQL 18.1, 17.7, 16.11, 15.15, 14.20, and 13.23 are affected.