The only thing I see that others have not mentioned falls into the 'never trust user input' category:

my $sequence_number = shift ||
    die "cinnamon: sequence number needed as argument\n";

open (ERROR, "/usr/bin/errpt -g -l $sequence_number |");
[download]

You're passing whatever the first parameter is directly to the open, and you're not checking to see if the open failed. Here's a modification with a little more paranoid error checking.

my $sequence_number = shift;
unless ($sequence_number =~ /^\d+$/) {
    # I am assuming it must be a number
    die "cinnamon: sequence number needed as argument\n";
}

open (ERROR, "/usr/bin/errpt -g -l $sequence_number |") || die "couldn
+'t open errpt: $!";
[download]

/\/\averick
perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"