Integer underflow in PostgreSQL ECPG allows a database server administrator to achieve temporary denial of service against the ECPG client via sending a byte value lacking the mandatory prefix. The client overwrites a huge memory region with bytes outside attacker knowledge or control. This typically yields a simple SIGSEV, 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.