The bitsubstr function in backend/utils/adt/varbit.c in PostgreSQL 8.0.23, 8.1.11, and 8.3.8 allows remote authenticated users to cause a denial of service (daemon crash) or have unspecified other impact via vectors involving a negative integer in the third argument, as demonstrated by a SELECT statement that contains a call to the substring function for a bit string, related to an "overflow."