Integer underflow in PostgreSQL ECPG allows a database server administrator to achieve temporary denial of service against the ECPG client via sending a bytea value lacking the mandatory prefix.  The client overwrites a huge memory region with bytes outside attacker knowledge or control.  This typically yields a simple SIGSEGV, but rare cases might achieve client-specific integrity impact via the write.  Versions before PostgreSQL 18.5, 17.11, 16.15, 15.19, and 14.24 are affected.