I don't have time to address this in depth, but I can at least explain the problem.

In the first pass of the outer loop, the inner loop reads SUMMARY to the end. Thus, in subsequent passes of the outer loop, the inner doesn't get executed since the file pointer is already at the end of the file.

You'll need to seek to the start of the file before the inner loop (poor choice), or load the summary file into memory before entering the outer loop (better choice).

By the way, there's never any reason to do foreach (<$fh>). Use while (<$fh>) instead.

Update: Assuming each line has a unique id,

#!/usr/bin/perl -w

use strict;

use Text::CSV_XS qw( );

@ARGV == 1
   or die("usage: $0 id\n");

my ($query_id) = @ARGV;

my $csv = Text::CSV_XS->new();

my $query_cve_id;
{
   my $map_qfn = 'vuln_cve_map.csv';
   open(my $map_fh, '<', $map_qfn)
      or die("Can't open mapping file \"$map_qfn\": $!\n");

   while (my $row = $csv->getline($map_fh)) {
      my ($id, $cve_id) = @$row;
      if ($id == $query) {
         $query_cve_id = $cve_id};
         last;
      }
   }
}

{
   my $summary_qfn = 'CVE_summary.csv';
   open(my $summary_fh, '<', $sumamry_qfn)
      or die("Can't open CVE Summary file \"$summary_qfn\": $!\n");

   while (my $row = $csv->getline($summary_fh)) {
      my ($cve_id, $summary) = @$row;
      if ($cve_id == $query_cve_id) {
         print("[$cve_id] $summary\n");
         last;
      }
  }
}
[download]