Libyal libpff through 20260926 contains an integer underflow in libpff_record_entry_get_multi_value() that allows attackers to trigger heap out-of-bounds reads via non-monotonic multi-value offsets. Attackers can craft PST, OST or PAB files with decreasing PT_MV_STRING8, PT_MV_UNICODE or PT_MV_BINARY offsets to crash libpff, pypff or pffexport and expose adjacent heap memory.