Process crash via dangling AWK field pointer

Use-after-free in the BusyBox 1.36.1 AWK applet allows local users to crash the process by running a crafted AWK program. While evaluating two field operands, evaluate() can let the right operand reallocate Fields after retaining a pointer to the left field, then pass that dangling pointer through getvar_s() to xasprintf(). Execution of attacker-controlled AWK input is required; the demonstrated consequence is a heap read from freed memory and process termination.