Out-of-bounds writes via base64 length overflow

Integer overflow in Apache APR-util 1.6.1 and earlier allows remote attackers to write beyond buffer bounds through oversized base64 input. The apr_base64 length routines compute encoded or decoded sizes in signed integers without rejecting inputs beyond representable limits, so callers can allocate an undersized output buffer before data is written. Reachability depends on a consuming application passing attacker-controlled, extremely large base64 data to these functions; resulting memory corruption can crash the process or alter memory.