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."