That code will work fine, but here is a variation that means you don't need to uncompress the complete outer zip into memory before accessing the inner one.

use warnings;
use strict;

use IO::Uncompress::Unzip qw(:all);

my $file1 = "all.zip";
my $file2 = "1.zip";

my $first = new IO::Uncompress::Unzip $file1
    or die "Cannot open $file1: $UnzipError\n";

my $output;
unzip $first => \$output
    or die "Cannot open $file2: $UnzipError\n";
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