+#!/usr/bin/perl
+
+# This cheak is based on code from the Debian/OpenSSL Weak Key Detector
+# written by Florian Weimer <fw@deneb.enyo.de>.
+# The code has been modified and enhanced by Alexander Wirt
+# <formorer@debian.org> to use it as a nagios check.
+#
+# Copyright (c) 2008, Florian Weimer <fw@deneb.enyo.de> for the original
+# Debian/OpenSSL Weak Key Detector
+# (http://security.debian.org/project/extra/dowkd/dowkd.pl.gz)
+#
+# Copyright (c) 2008, Alexander Wirt <formorer@debian.org> for check_weakkeys
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+#
+
+=pod
+
+=head1 NAME
+
+B<check_weakkeys> - checks system for weak ssh keys
+
+=cut
+
+=head1 SYNOPSIS
+
+B<check_weakkeys> [options]
+
+=cut
+
+=head1 DESCRIPTION
+
+B<check_weakkeys> checks for all users if there id_rsa, id_dsa or
+authorized_key files if they contain weak ssh keys created by a Debian with a
+broken libssl (see DSA-1571 for more informations). Optionally <check_weakkeys>
+can spit out a warning of there are any DSA keys left in key or authorized_key
+files. To work it needs a database of precomputed hashes of known weak keys.
+This file is expected as an bdb database with the hash (like
+03:a2:f0:46:7f:13:9f:5f:96:71:a9:b8:a0:1c:01:05) as key. See <gen_fprdb> for
+such a database generator. <check_weakkeys> outputs his data to STDOUT or to a
+file. It meaned to be picked up by an nagios check like B<dsa-check-statusfile>
+from Peter Palfrader.
+
+=cut
+
+=head1 OPTIONS
+
+=over 4
+
+=item B<-h, --help>
+
+Prints out a brief help
+
+=item B<-s, --statusfile> "statusfile"
+
+Use 'F<statusfile>' instead of 'F<STDOUT>'.
+
+=item B<-f, --fprdb> "database" (default: /var/lib/dsa/ssh-weak-keys.db)
+
+Use 'F<database>' instead of 'F</var/lib/dsa/ssh-weak-keys.db>'
+as fingerprint database.
+
+=item B<-n, --dsa_nowarn>
+
+Don't warn for DSA keys
+
+=back
+
+=cut
+
+use strict;
+use warnings;
+
+use File::Temp;
+use BerkeleyDB;
+use Pod::Usage;
+use Getopt::Long;
+use IPC::Open3;
+
+my $fprdb_fname = "/var/lib/dsa/ssh-weak-keys.db" ;
+my ($outfile, $help);
+my $dsa_nowarn = 0;
+
+GetOptions( 'help|h' => \$help, #Help function
+ 'statusfile|s=s' => \$outfile,
+ 'fprdb|f=s' => \$fprdb_fname,
+ 'n|dsa_nowarn' => \$dsa_nowarn,
+);
+
+pod2usage(1) if $help;
+
+my $fh;
+if ($outfile) {
+ open ($fh, '>', $outfile)
+ or die "Could not open statusfile '$outfile' for writing: $!";
+} else {
+ $fh = *STDOUT;
+}
+
+my %fpr_hash;
+tie %fpr_hash, 'BerkeleyDB::Btree',
+ -Filename => $fprdb_fname,
+ -Flags => DB_RDONLY
+ or die "Cannot open fingerprint db $fprdb_fname: $! $BerkeleyDB::Error\n";
+
+
+my ($weak_keys,$checked_keys) = 0;
+my $dsa_keys = 0;
+my $text = '';
+my %key_sizes;
+
+
+
+&from_user_all;
+&from_ssh_host(qw(localhost));
+
+my $status="OK";
+if ($weak_keys) {
+ $status = "CRITICAL";
+} elsif ($dsa_keys && ! $dsa_nowarn) {
+ $status = "WARNING";
+}
+
+print $fh "$status\n";
+print $fh "Checked $checked_keys keys - $weak_keys weak - $dsa_keys dsa keys\n";
+print $fh "Sizes: ";
+foreach my $size (sort(keys(%key_sizes))) {
+ print $fh "$size:$key_sizes{$size} ";
+}
+
+print $fh "\n";
+print $fh "$text" if $text;
+
+
+
+sub safe_backtick (@) {
+ my @args = @_;
+
+ my ($wtr, $fh, $err);
+
+ open3($wtr,$fh,$err, @args)
+ or die "error: failed to spawn $args[0]: $!\n";
+ my @result;
+ if (wantarray) {
+ @result = <$fh>;
+ } else {
+ local $/;
+ @result = scalar(<$fh>);
+ }
+ close $fh;
+ $? == 0 or return undef;
+ if (wantarray) {
+ return @result;
+ } else {
+ return $result[0];
+ }
+}
+
+sub ssh_fprint_file ($) {
+ my $name = shift;
+ my $data = safe_backtick qw/ssh-keygen -l -f/, $name;
+ defined $data or return ();
+ my @data = $data =~ /^(\d+) ([0-9a-f]{2}(?::[0-9a-f]{2}){15})/;
+ return @data if @data == 2;
+ return ();
+}
+
+sub ssh_fprint_check ($$$) {
+ my ($name, $length, $hash) = @_;
+ if (exists $key_sizes{$length}) {
+ $key_sizes{$length}++;
+ } else {
+ $key_sizes{$length}=1;
+ }
+ $checked_keys++;
+ if (exists $fpr_hash{$hash}) {
+ $weak_keys++;
+ $text .= "$name weak ($hash)\n";
+ }
+}
+
+
+sub from_ssh_key_file ($) {
+ my $name = shift;
+ if (open (my $FH, '<', $name)) {
+ my $key = <$FH>;
+ if ($key =~ m/^ssh-dss/) {
+ $dsa_keys++;
+ $text .= "$name is a DSA key\n";
+ }
+ } else {
+ $text .= "Could not open $name: $!";
+ }
+ my ($length, $hash) = ssh_fprint_file $name;
+ if ($length && $hash) {
+ ssh_fprint_check "$name:1", $length, $hash;
+ } else {
+ $text .= "$name:1: warning: failed to parse SSH key file\n";
+ }
+}
+
+sub clear_tmp ($) {
+ my $tmp = shift;
+ seek $tmp, 0, 0 or die "seek: $!";
+ truncate $tmp, 0 or die "truncate: $!";
+}
+
+sub from_ssh_auth_file ($) {
+ my $name = shift;
+ my $auth;
+ unless (open $auth, '<', $name) {
+ warn "$name:0: error: open failed: $!\n";
+ return;
+ }
+ my $tmp = new File::Temp;
+ while (my $line = <$auth>) {
+ chomp $line;
+ my $lineno = $.;
+ clear_tmp $tmp;
+ next if $line =~ m/^#/; # ignore comments
+ if ($line =~ m/^ssh-dss/) {
+ $dsa_keys++;
+ $text .= "$name:$lineno is a DSA key\n";
+ }
+ print $tmp "$line\n" or die "print: $!";
+ $tmp->flush;
+ my ($length, $hash) = ssh_fprint_file "$tmp";
+ if ($length && $hash) {
+ ssh_fprint_check "$name:$lineno", $length, $hash;
+ } else {
+ $text .= "$name:$lineno: warning: unparsable line\n";
+ }
+ }
+}
+
+sub from_ssh_host (@) {
+ my @names = @_;
+ my @lines;
+ push @lines, safe_backtick qw|ssh-keyscan -t rsa|, @names;
+ push @lines, safe_backtick qw|ssh-keyscan -t dsa|, @names;
+
+ my $tmp = new File::Temp;
+ for my $line (@lines) {
+ next if $line =~ /^#/;
+ my ($host, $data) = $line =~ /^(\S+) (.*)$/;
+ clear_tmp $tmp;
+ print $tmp "$data\n" or die "print: $!";
+ $tmp->flush;
+ my ($length, $hash) = ssh_fprint_file "$tmp";
+ if ($length && $hash) {
+ ssh_fprint_check "$host", $length, $hash;
+ } else {
+ $text .= "$host: warning: unparsable line\n";
+ }
+ }
+}
+
+sub from_user ($) {
+ my $user = shift;
+ my ($name,$passwd,$uid,$gid,
+ $quota,$comment,$gcos,$dir,$shell,$expire) = getpwnam($user);
+ my $file = "$dir/.ssh/authorized_keys";
+ from_ssh_auth_file $file if -r $file;
+ $file = "$dir/.ssh/authorized_keys2";
+ from_ssh_auth_file $file if -r $file;
+ $file = "$dir/.ssh/id_rsa.pub";
+ from_ssh_key_file $file if -r $file;
+ $file = "$dir/.ssh/id_dsa.pub";
+ from_ssh_key_file $file if -r $file;
+}
+
+sub from_user_all () {
+ setpwent;
+ while (my $name = getpwent) {
+ from_user $name;
+ }
+ endpwent;
+}
+
+
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