psqlODBC sizes its row cache from the column count of a cursor's first result, but recomputes the column count from each later FETCH reply without checking that it matches. A server not trusted under current SSL settings can answer a later FETCH with more columns and make the driver write tuple records past the end of the heap allocation. A keyset reply with fewer columns than the key fields also underflows the unsigned field count. This is reachable with UseDeclareFetch enabled. Versions before psqlODBC 18.00.0006 are affected.