dowkd.in

   1 #!/usr/bin/perl
   2
   3 # Debian/OpenSSL Weak Key Detector
   4 #
   5 # Copyright (C) 2008, Florian Weimer <fw@deneb.enyo.de>
   6 #
   7 # Permission to use, copy, modify, and distribute this software for
   8 # any purpose with or without fee is hereby granted, provided that the
   9 # above copyright notice and this permission notice appear in all
  10 # copies.
  11 #
  12 # THE SOFTWARE IS PROVIDED "AS IS" AND FLORIAN WEIMER AND HIS
  13 # CONTRIBUTORS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
  14 # INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.  IN
  15 # NO EVENT SHALL FLORIAN WEIMER OR HIS CONTRIBUTORS BE LIABLE FOR ANY
  16 # SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  17 # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
  18 # AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
  19 # OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  20 # SOFTWARE.
  21 #
  22 # Blacklist data has been provided by Kees Cook, Peter Palfrader and
  23 # James Strandboge.
  24 #
  25 # Patches and comments are welcome.  Please send them to
  26 # <fw@deneb.enyo.de>, and use "dowkd" in the subject line.
  27 #
  28 # This version is based on commit @PROGRAM_SHA1@
  29 # in the GIT repository at <http://repo.or.cz/w/dowkd.git>.
  30
  31 use strict;
  32 use warnings;
  33
  34 sub help () {
  35     print <<EOF;
  36 usage: $0 [OPTIONS...] COMMAND [ARGUMENTS...]
  37
  38 COMMAND is one of:
  39
  40   file:  examine files on the command line for weak keys
  41   host:  examine the specified hosts for weak SSH keys
  42          (change destination port with "host -p PORT HOST...")
  43   user:  examine user SSH keys for weakness; examine all users if no
  44          users are given
  45   quick: check this host for weak keys (encompasses "user" plus
  46          heuristics to find keys in /etc)
  47   help:  show this help screen
  48   version: show version information
  49
  50 OPTIONS is one of:
  51
  52   -c FILE: set the database cache file name (default: dowkd.db)
  53
  54 dowkd currently handles the following OpenSSH host and user keys,
  55 provided they have been generated on a little-endian architecture
  56 (such as i386 or amd64):
  57
  58   RSA/1024, RSA/2048, RSA1/1024, RSA1/2048
  59   RSA/4096
  60   DSA/1024
  61
  62 (The relevant OpenSSH versions in Debian do not support DSA key
  63 generation with other sizes.)
  64
  65 OpenVPN shared also detected if they have been created on
  66 little-endian architectures.
  67
  68 Unencrypted RSA private keys and PEM certificate files generated by
  69 OpenSSL are detected, provided they use key lengths of 1024 or 2048
  70 bits (again, only for little-endian architectures).
  71
  72 Note that the blacklist by dowkd may be incomplete; it is only
  73 intended as a quick check.
  74
  75 EOF
  76 }
  77
  78 use DB_File;
  79 use File::Temp;
  80 use Fcntl;
  81 use IO::Handle;
  82
  83 my $db_version = '@DB_VERSION@';
  84 my $program_version = '@PROGRAM_VERSION@';
  85 my $changelog = <<'EOF';
  86 ChangeLog:
  87 @CHANGELOG@
  88 EOF
  89
  90 my $db_file = 'dowkd.db';
  91
  92 my $db;
  93 my %db;
  94
  95 sub create_db () {
  96     warn "notice: creating database, please wait\n";
  97     $db = tie %db, 'DB_File', $db_file, O_RDWR | O_CREAT, 0777, $DB_BTREE
  98         or die "error: could not open database: $!\n";
  99
 100     my $found;
 101     while (my $line = <DATA>) {
 102         next if $line =~ /^\**$/;
 103         chomp $line;
 104         $line =~ /^[0-9a-f]{32}$/ or die "error: invalid data line";
 105         $line =~ s/(..)/chr(hex($1))/ge;
 106         $db{$line} = '';
 107         $found = 1;
 108     }
 109     $found or die "error: no blacklist data found in script\n";
 110
 111     # Set at the end so that no incomplete database is left behind.
 112     $db{''} = $db_version;
 113
 114     $db->sync;
 115 }
 116
 117 sub open_db () {
 118     if (-r $db_file) {
 119         $db = tie %db, 'DB_File', $db_file, O_RDONLY, 0777, $DB_BTREE
 120             or die "error: could not open database: $!\n";
 121         my $stored_version = $db{''};
 122         $stored_version && $stored_version eq $db_version or create_db;
 123     } else {
 124         unlink $db_file;
 125         create_db;
 126     }
 127 }
 128
 129 sub safe_backtick (@) {
 130     my @args = @_;
 131     my $fh;
 132     open $fh, '-|', @args
 133         or die "error: failed to spawn $args[0]: $!\n";
 134     my @result;
 135     if (wantarray) {
 136         @result = <$fh>;
 137     } else {
 138         local $/;
 139         @result = scalar(<$fh>);
 140     }
 141     close $fh;
 142     $? == 0 or return undef;
 143     if (wantarray) {
 144         return @result;
 145     } else {
 146         return $result[0];
 147     }
 148 }
 149
 150 sub safe_backtick_stderr {
 151     my @args = @_;
 152     my $fh;
 153     my $pid = open $fh, '-|';
 154     if ($pid) {
 155         my @result = <$fh>;
 156         close $fh;
 157         $? == 0 or return undef;
 158         if (wantarray) {
 159             return @result;
 160         } else {
 161             return join('', @result);
 162         }
 163     } else {
 164         open STDERR, '>&STDOUT' or die "error: could not redirect stderr: $!";
 165         exec @args or die "exec: failed: $!";
 166     }
 167 }
 168
 169 my $keys_found = 0;
 170 my $keys_vulnerable = 0;
 171
 172 sub print_stats () {
 173     print STDERR "summary: keys found: $keys_found, weak keys: $keys_vulnerable\n";
 174 }
 175
 176 sub check_hash ($$;$) {
 177     my ($name, $hash, $descr) = @_;
 178     ++$keys_found;
 179     if (exists $db{$hash}) {
 180         ++$keys_vulnerable;
 181         $descr = $descr ? " ($descr)" : '';
 182         print "$name: weak key$descr\n";
 183     }
 184 }
 185
 186 sub ssh_fprint_file ($) {
 187     my $name = shift;
 188     my $data = safe_backtick qw/ssh-keygen -l -f/, $name;
 189     defined $data or return ();
 190     my @data = $data =~ /^(\d+) ([0-9a-f]{2}(?::[0-9a-f]{2}){15})/;
 191     return @data if @data == 2;
 192     return ();
 193 }
 194
 195 sub ssh_fprint_check ($$$$) {
 196     my ($name, $type, $length, $hash) = @_;
 197     $type =~ /^(?:rsa1?|dsa)\z/ or die;
 198     if (($type eq 'rsa'
 199          && ($length == 1024 || $length == 2048 || $length == 4096))
 200         || ($type eq 'dsa' && $length == 1024)
 201         || ($type eq 'rsa1' && ($length == 1024 || $length == 2048))) {
 202         $hash =~ y/://d;
 203         $hash =~ s/(..)/chr(hex($1))/ge;
 204         check_hash $name, $hash, "OpenSSH/$type/$length";
 205     } elsif ($type eq 'dsa') {
 206         print "$name: $length bits DSA key not recommended\n";
 207     } else {
 208         warn "$name: warning: no blacklist for $type/$length key\n";
 209     }
 210 }
 211
 212 sub clear_tmp ($) {
 213     my $tmp = shift;
 214     seek $tmp, 0, 0 or die "seek: $!";
 215     truncate $tmp, 0 or die "truncate: $!";
 216 }
 217
 218 sub cleanup_ssh_auth_line ($) {
 219     my $line = shift;
 220
 221     $line =~ /^(?:ssh-(?:rsa|dss)\s|\d+\s+\d+\s+\d)/ and return $line;
 222
 223   OUTSIDE_STRING:
 224     if ($line =~ /^\s+(.*)/) {
 225         $line = $1;
 226         goto SPACE_SEEN;
 227     }
 228     if ($line =~ /^"(.*)/) {
 229         $line = $1;
 230         goto INSIDE_STRING;
 231     }
 232     if ($line =~ /^\\.(.*)/) {
 233         # It doesn't matter if we don't deal with \000 properly, we
 234         # just need to defuse the backslash character.
 235         $line = $1;
 236         goto OUTSIDE_STRING;
 237     }
 238     if ($line =~ /^[a-zA-Z0-9_=+-]+(.*)/) {
 239         # Skip multiple harmless characters in one go.
 240         $line = $1;
 241         goto OUTSIDE_STRING;
 242     }
 243     if ($line =~ /^.(.*)/) {
 244         # Other characters are stripped one by one.
 245         $line = $1;
 246         goto OUTSIDE_STRING;
 247     }
 248     return undef;               # empty string, no key found
 249
 250   INSIDE_STRING:
 251     if ($line =~ /^"(.*)/) {
 252         $line = $1;
 253         goto OUTSIDE_STRING;
 254     }
 255     if ($line =~ /^\\.(.*)/) {
 256         # See above, defuse the backslash.
 257         $line = $1;
 258         goto INSIDE_STRING;
 259     }
 260     if ($line =~ /^[^\\"]+(.*)/) {
 261         $line = $1;
 262         goto INSIDE_STRING;
 263     }
 264     return undef;               # missing closing double quote
 265
 266   SPACE_SEEN:
 267     $line =~ /^(?:ssh-(?:rsa|dss)\s|\d+\s+\d+\s+\d)/ and return $line;
 268     return undef;
 269 }
 270
 271 sub derive_ssh_auth_type ($) {
 272     my $line = shift;
 273     $line =~ /^ssh-rsa\s/ and return 'rsa';
 274     $line =~ /^ssh-dss\s/ and return 'dsa';
 275     $line =~ /^\d+\s/ and return 'rsa1';
 276     return undef;
 277 }
 278
 279 sub from_ssh_auth_line ($$$) {
 280     my ($tmp, $name, $line) = @_;
 281     chomp $line;
 282
 283     {
 284         my $l = cleanup_ssh_auth_line $line;
 285         $l or return 0;
 286         $line = $l;
 287     }
 288     my $type = derive_ssh_auth_type $line;
 289
 290     clear_tmp $tmp;
 291     print $tmp "$line\n" or die "print: $!";
 292     $tmp->flush or die "flush: $!";
 293     my ($length, $hash) = ssh_fprint_file "$tmp";
 294     if ($length && $hash) {
 295         ssh_fprint_check "$name", $type, $length, $hash;
 296         return 1;
 297     }
 298
 299     return 0;
 300 }
 301
 302 sub from_ssh_auth_file ($) {
 303     my $name = shift;
 304     my $auth;
 305     unless (open $auth, '<', $name) {
 306         warn "$name:0: error: open failed: $!\n";
 307         return;
 308     }
 309
 310     my $tmp = new File::Temp;
 311     my $last_status = 1;
 312     while (my $line = <$auth>) {
 313         next if $line =~ m/^\s*(#|$)/;
 314         my $status = from_ssh_auth_line $tmp, "$name:$.", $line;
 315         unless ($status) {
 316             $last_status and warn "$name:$.: warning: unparsable line\n";
 317         }
 318         $last_status = $status;
 319     }
 320 }
 321
 322 sub from_openvpn_key ($) {
 323     my $name = shift;
 324     my $key;
 325     unless (open $key, '<', $name) {
 326         warn "$name:0: open failed: $!\n";
 327         return 1;
 328     }
 329
 330     my $marker;
 331     while (my $line = <$key>) {
 332         return 0 if $. > 10;
 333         if ($line =~ /^-----BEGIN OpenVPN Static key V1-----/) {
 334             $marker = 1;
 335         } elsif ($marker) {
 336             if ($line =~ /^([0-9a-f]{32})/) {
 337                 $line = $1;
 338                 $line =~ s/(..)/chr(hex($1))/ge;
 339                 check_hash "$name:$.", $line, "OpenVPN";
 340                 return 1;
 341             } else {
 342                 warn "$name:$.: warning: illegal OpenVPN file format\n";
 343                 return 1;
 344             }
 345         }
 346     }
 347 }
 348
 349 sub openssl_modulus_check ($$) {
 350     my ($name, $modulus) = @_;
 351     chomp $modulus;
 352     if ($modulus =~ /^Modulus=([A-F0-9]+)$/) {
 353         $modulus = $1;
 354         my $length = length($modulus) * 4;
 355         if ($length == 1024 || $length == 2048) {
 356             my $mod = substr $modulus, length($modulus) - 32;
 357             $mod =~ y/A-F/a-f/;
 358             my @mod = $mod =~ /(..)/g;
 359             $mod = join('', map { chr(hex($_)) } reverse @mod);
 360             check_hash $name, $mod, "OpenSSL/RSA/$length";
 361         } else {
 362             warn "$name: warning: no blacklist for OpenSSL/RSA/$length key\n";
 363         }
 364     } else {
 365         die "internal error: $modulus\n";
 366     }
 367 }
 368
 369 sub from_pem ($) {
 370     my $name = shift;
 371     my $tmp;
 372     my $found = 0;
 373
 374     my $src;
 375     unless (open $src, '<', $name) {
 376         warn "$name:0: open failed: $!\n";
 377         return 1;
 378     }
 379
 380     while (my $line = <$src>) {
 381         if ($line =~ /^-----BEGIN CERTIFICATE-----/) {
 382             my $lineno = $.;
 383             $tmp or $tmp = new File::Temp;
 384             clear_tmp $tmp;
 385             do {
 386                 print $tmp $line or die "print: $!";
 387                 goto LAST if $line =~ /^-----END CERTIFICATE-----/;
 388             } while ($line = <$src>);
 389           LAST:
 390             $tmp->flush or die "flush: $!";
 391             my $mod = safe_backtick qw/openssl x509 -noout -modulus -in/, $tmp;
 392             if ($mod) {
 393                 openssl_modulus_check "$name:$lineno", $mod;
 394                 $found = 1;
 395             } else {
 396                 warn "$name:$lineno: failed to parse certificate\n";
 397                 return 1;
 398             }
 399         } elsif ($line =~ /^-----BEGIN RSA PRIVATE KEY-----/) {
 400             my $lineno = $.;
 401             $tmp or $tmp = new File::Temp;
 402             clear_tmp $tmp;
 403             do {
 404                 print $tmp $line or die "print: $!";
 405                 goto LAST_RSA if $line =~ /^-----END RSA PRIVATE KEY-----/;
 406             } while ($line = <$src>);
 407           LAST_RSA:
 408             $tmp->flush or die "flush: $!";
 409             my $mod = safe_backtick qw/openssl rsa -noout -modulus -in/, $tmp;
 410             if ($mod) {
 411                 openssl_modulus_check "$name:$lineno", $mod;
 412                 $found = 1;
 413             } else {
 414                 warn "$name:$lineno: failed to parse RSA private key\n";
 415                 return 1;
 416             }
 417         }
 418     }
 419
 420     return $found;
 421 }
 422
 423 sub from_ssh_host ($@) {
 424     my ($port, @names) = @_;
 425
 426     @names = grep {
 427         my ($name,$aliases,$addrtype,$length,@addrs) = gethostbyname $_;
 428         @addrs or warn "warning: host not found: $_\n";
 429         @addrs > 0;
 430     } @names;
 431
 432     my @lines= safe_backtick_stderr qw/ssh-keyscan -t/, 'rsa1,rsa,dsa',
 433         '-p', $port, @names;
 434
 435     my $tmp = new File::Temp;
 436     for my $line (@lines) {
 437         next if $line =~ /^(?:#|no hostkey alg)/;
 438         my ($host, $data) = $line =~ /^(\S+) (.*)$/;
 439         $host && from_ssh_auth_line $tmp, $host, $data
 440             or die "$host: warning: unparsable line: $line";
 441     }
 442 }
 443
 444 sub from_user ($) {
 445     my $user = shift;
 446     my ($name,$passwd,$uid,$gid,
 447         $quota,$comment,$gcos,$dir,$shell,$expire) = getpwnam($user);
 448     unless ($name) {
 449         warn "warning: user $user does not exist\n";
 450         return;
 451     }
 452     for my $name (qw/authorized_keys authorized_keys2
 453                      known_hosts known_hosts2
 454                      id_rsa.pub id_dsa.pub identity.pub/) {
 455         my $file = "$dir/.ssh/$name";
 456         from_ssh_auth_file $file if -r $file;
 457     }
 458 }
 459
 460 sub from_user_all () {
 461     # This was one loop initially, but does not work with some Perl
 462     # versions.
 463     setpwent;
 464     my @names;
 465     while (my $name = getpwent) {
 466         push @names, $name;
 467     }
 468     endpwent;
 469     from_user $_ for @names;
 470 }
 471
 472 sub from_any_file ($) {
 473     my $name = shift;
 474     from_openvpn_key $name and return;
 475     from_pem $name and return;
 476     from_ssh_auth_file $name;
 477 }
 478
 479 sub from_etc () {
 480     my $find;
 481     open $find, '-|', qw!find /etc -type f (
 482             -name *.key -o -name *.pem -o -name *.crt
 483         ) -print0! or die "error: could not spawn find: $!";
 484     my @files;
 485     {
 486         local $/ = "\0";
 487         @files = <$find>;
 488     }
 489     close $find;
 490     $? == 0 or die "error: find failed with exit status $?\n";
 491     for my $file (@files) {
 492         -e $file and from_any_file $file;
 493     }
 494 }
 495
 496 if (@ARGV && $ARGV[0] eq '-c') {
 497     shift @ARGV;
 498     $db_file = shift @ARGV if @ARGV;
 499 }
 500 if (@ARGV) {
 501     open_db;
 502     my $cmd = shift @ARGV;
 503     if ($cmd eq 'file') {
 504         for my $name (@ARGV) {
 505             from_any_file $name;
 506         }
 507     } elsif ($cmd eq 'host') {
 508         unless (@ARGV) {
 509             help;
 510             exit 1;
 511         }
 512         my $port = 22;
 513         if ($ARGV[0] eq '-p') {
 514             shift @ARGV;
 515             if (@ARGV) {
 516                 $port = shift @ARGV;
 517             }
 518         } elsif ($ARGV[0] =~ /-p(\d+)/) {
 519             $port = $1;
 520             shift @ARGV;
 521         }
 522         unless (@ARGV) {
 523             help;
 524             exit 1;
 525         }
 526         from_ssh_host $port, @ARGV;
 527     } elsif ($cmd eq 'user') {
 528         if (@ARGV) {
 529             from_user $_ for @ARGV;
 530         } else {
 531             from_user_all;
 532         }
 533     } elsif ($cmd eq 'quick') {
 534         from_user_all;
 535         for my $file (qw/ssh_host_rsa_key.pub ssh_host_dsa_key.pub
 536                         ssh_host_key ssh_known_hosts ssh_known_hosts2/) {
 537             -e $file and from_ssh_auth_file $file;
 538         }
 539         from_etc;
 540     } elsif ($cmd eq 'help') {
 541         help;
 542         exit 0;
 543     } elsif ($cmd eq 'version') {
 544         print "dowkd $program_version (database $db_version)\n\n$changelog";
 545         exit 0;
 546     } else {
 547         die "error: invalid command, use \"help\" to get help\n";
 548     }
 549     print_stats;
 550 } else {
 551     help;
 552     exit 1;
 553 }
 554
 555 my %hash;
 556
 557 __DATA__