rapidcsv is a C++ CSV parser library. Prior to 8.99, RemoveColumn, InsertColumn, RemoveRow, InsertRow, and GetColumnNames converted sizet indexes to int before adding them to std::vector iterators. On 64-bit systems, in a CSV matrix dimension containing more than 2^31 elements, an index above INTMAX could wrap to a negative iterator offset and point before the start of the vector, causing undefined behavior, heap memory corruption, or a crash. Triggering the issue requires an extremely large in-memory document, requiring tens of gigabytes of memory at minimum, so typical CSV documents are not practically affected. This issue is fixed in version 8.99.