Here's the code with some fixed typos and with error checking.

#!/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_id) {
         $query_cve_id = $cve_id;
         last;
      }
   }

   if ($csv->error_diag()) {
      die("Can't parse mapping file: ", $csv->error_diag(), "\n");
   }
}

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

   if ($csv->error_diag()) {
      die("Can't parse CVE Summary file: ", $csv->error_diag(), "\n");
   }
}
[download]

Running it yields

Can't parse CVE Summary file: 2021EIQ - NL char inside quotes, binary 
+off58
[download]

Your data is bad.

"CVE-1999-0095","The debug command in Sendmail is enabled
                                                         ^
                                                         |
                                                      missing
                                                      closing
                                                       quote
[download]

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