nagios-plugins/plugins-scripts/check_ssl_validity.pl

#! /usr/bin/perl
# nagios: -epn

# Complete (?) check for valid SSL certificate
# Originally by Anders Nordby (anders@fupp.net), 2015-02-16
# Copied with permission on 2019-09-26 (https://github.com/nagios-plugins/nagios-plugins/issues/72)
# and modified to fit the needs of the nagios-plugins project.

# Copyright: GPLv2

# Checks all of the following:
# Fetch SSL certificate from URL (on optional given host)
# Does the certificate contain our hostname?
# Has the certificate expired?
# Download (and cache) CRL
# Has the certificate been revoked?

use Getopt::Std;
use File::Temp qw(tempfile);
use Crypt::X509;
use Date::Parse;
use POSIX qw(strftime);
use Digest::MD5 qw(md5_hex);
use LWP::Simple;

getopts('p:t:H:dw:c:I:C:d');

sub usage {
        print "check_ssl_validity -H <cert hostname> [-I <IP/host>] [-p <port>]\n[-t <timeout>] [-w <expire warning (days)>] [-c <expire critical (dats)>]\n[-C (CRL update frequency in seconds)] [-d (debug)]\n";
        print "\nWill look for hostname provided with -H in the certificate, but will contact\n";
        print "server with host/IP provided by -I (optional)\n";
        exit(1);
}

sub updatecrl {
    my $url = shift;
    my $fn = shift;

    my $content = get($url);
    if (defined($content)) {
        if (open(CACHE, ">$cachefile")) {
            print CACHE $content;
        } else {
            doexit(2, "Could not open file $fn for writing CRL temp file for cert on $host:$port.");
        }
        close(CACHE);
    } else {
        doexit(2, "Could not download CRL Distribution Point URL $url for cert on $hosttxt.");
    }
}

sub ckserial {
    return if ($crserial eq "");
    if ($serial eq $crserial) {
        if ($crrev ne "") {
            $crrevtime = str2time($crrev);
            $revtime = $crrevtime-$uxtime;
            if ($revtime < 0) {
                doexit(2, "Found certificate for $vhost on CRL $crldp revoked already at date $crrev");
            } elsif (($revtime/86400) < $crit) {
                doexit(2, "Found certificate for $vhost on CRL $crldp revoked at date $crrev, within critical time frame $crit");
            } elsif (($revtime/86400) < $warn) {
                doexit(1, "Found certificate for $vhost on CRL $crldp revoked at date $crrev, within warning time frame $warn");
            }
        }
        doexit(1, "Found certificate for $vhost on CRL $crldp revoked $crrev. Time to check the revokation date");
    }
}

usage unless ($opt_H);

# Defaults
if ($opt_p) {
        $port = $opt_p;
} else {
        $port = 443;
}

if ($opt_t) {
        $tmout = $opt_t;
} else {
        $tmout = 10;
}

if ($opt_C) {
    $crlupdatefreq = $opt_C;
} else {
    $crlupdatefreq = 86400;
}

$vhost = $opt_H;
if ($opt_I) {
    $host = $opt_I;
} else {
    $host = $vhost;
}
$hosttxt = "$host:$port";

if ($opt_w && $opt_w =~ /^\d+$/) {
    $warn = $opt_w;
} else {
    $warn = 30;
}
if ($opt_c && $opt_c =~ /^\d+$/) {
    $crit = $opt_c;
} else {
    $crit = 30;
}

sub doexit {
        my $ret = shift;
        my $txt = shift;
        print "$txt\n";
        exit($ret);
}

$alldata = "";
$cert = "";
$mode = 0;
open(CMD, "echo | openssl s_client -servername $vhost -connect $host:$port 2>&1 |");
while (<CMD>) {
    $alldata .= $_;
    if ($mode == 0) {
        if (/-----BEGIN CERTIFICATE-----/) {
            $cert .= $_;
            $mode = 1;
        }
    } elsif ($mode == 1) {
        $cert .= $_;
        if (/-----END CERTIFICATE-----/) {
            $mode = 2;
        }
    }
}
close(CMD);
$ret = $?;
if ($ret != 0) {
    $alldata =~ s@\n@ @g;
    $alldata =~ s@\s+$@@;
    doexit(2, "Error connecting to $hosttxt: $alldata");
} elsif ($cert eq "") {
    doexit(2, "No certificate found on $hosttxt");
} else {
    ($tmpfh,$tempfile) = tempfile(DIR=>'/tmp',UNLINK=>0);
    doexit(2, "Failed to open temp file: $!") unless (defined($tmpfh));
    $tmpfh->print($cert);
    $tmpfh->close;
}

$dercert = `openssl x509 -in $tempfile -outform DER 2>&1`;
$ret = $?;
if ($ret != 0) {
    $dercert =~ s@\n@ @g;
    $dercert =~ s@\s+$@@;
    doexit(2, "Could not convert certificate from PEM to DER format: $dercert");
}

$decoded = Crypt::X509->new( cert => $dercert );
if ($decoded->error) {
    doexit(2, "Could not parse X509 certificate on $hosttxt: " . $decoded->error);
}

$oktxt = "";
$cn = $decoded->subject_cn;
if ($opt_d) { print "Found CN: $cn\n"; }
if ($vhost eq $decoded->subject_cn) {
	$oktxt .= "Host $vhost matches CN $vhost on $hosttxt ";
} elsif ($decoded->subject_cn =~ /^*\.(.*)$/) {
	$wcdomain = $1;
	$domain = $vhost;
	$domain =~ s@^[\w\-]+\.@@;
	if ($domain eq $wcdomain) {
		$oktxt .= "Host $vhost matches wildcard CN " . $decoded->subject_cn . " on $hosttxt ";
	}
}

if ($oktxt eq "") {
    # Cert not yet found
    if (defined($decoded->SubjectAltName)) {
        # Check altnames
        $altfound = 0;
        foreach $altnametxt (@{$decoded->SubjectAltName}) {
            if ($altnametxt =~ /^dNSName=(.*)/) {
                $altname = $1;
                if ($opt_d) { print "Found SAN: $altname\n"; }
                if ($vhost eq $altname) {
                    $altfound = 1;
                    $oktxt .= "Host $vhost found in SAN on $hosttxt ";
                    last;
                }
            }
        }
        if ($altfound == 0) {
            doexit(2, "Host $vhost not found in certificate on $hosttxt, not in CN or in alternative names");
        }
    } else {
        doexit(2, "Host $vhost not found in certificate on $hosttxt, not in CN and no alternative names found");
    }
}

# Check expire time
$uxtimegmt = strftime "%s", gmtime;
$uxtime = strftime "%s", localtime;
$certtime = $decoded->not_after;
$certdays = ($certtime-$uxtimegmt)/86400;
$certdaysfmt = sprintf("%.1f", $certdays);

if ($certdays < $crit) {
    doexit(2, "${oktxt}but it is expiring in only $certdaysfmt days, critical limit is $crit.");
} elsif ($certdays < $warn) {
    doexit(1, "${oktxt}but it is expiring in only $certdaysfmt days, warning limit is $warn.");
}

$serial = $decoded->serial;
$serial = lc(sprintf("%x", $serial));
if ($opt_d) {
    print "Certificate serial: $serial\n";
}
@crldps = @{$decoded->CRLDistributionPoints};
$crlskip = 0;
foreach $crldp (@crldps) {
    if ($opt_d) {
        print "Checking CRL DP $crldp.\n";
    }
    $cachefile = "/tmp/" . md5_hex($crldp) . "_crl.tmp";
    if (-f $cachefile) {
        $cacheage = $uxtime-(stat($cachefile))[9];
        if ($cacheage > $crlupdatefreq) {
            if ($opt_d) { print "Download update, more than a day old.\n"; }
            updatecrl($crldp, $cachefile);
        } else {
            if ($opt_d) { print "Reusing cached copy.\n"; }
        }
    } else {
        if ($opt_d) { print "Download initial copy.\n"; }
        updatecrl($crldp, $cachefile);
    }

    $crl = "";
    my $format;
    open(my $cachefile_io, '<', $cachefile);
    $format = <$cachefile_io> =~ /-----BEGIN X509 CRL-----/ ? 'PEM' : 'DER';
    close $cachefile_io;
    open(CMD, "openssl crl -inform $format -text -in $cachefile -noout 2>&1 |");
    while (<CMD>) {
        $crl .= $_;
    }
    close(CMD);
    $ret = $?;
    if ($ret != 0) {
        $crl =~ s@\n@ @g;
        $crl =~ s@\s+$@@;
        doexit(2, "Could not parse $format from URL $crldp while checking $hosttxt: $crl");
    }

    # Crude CRL parsing goes here
    $mode = 0;
    foreach $cline (split(/\n/, $crl)) {
        if ($cline =~ /.*Next Update: (.+)/) {
            $nextup = $1;
            $nextuptime = str2time($nextup);
            $crlvalid = $nextuptime-$uxtime;
            if ($opt_d) { print "Next CRL update: $nextup\n"; }
            if ($crlvalid < 0) {
                doexit(2, "Could not use CRL from $crldp, it expired past next update on $nextup");
            }
        } elsif ($cline =~ /.*Last Update: (.+)/) {
            $lastup = $1;
            if ($opt_d) { print "Last CRL update: $lastup\n"; }
        } elsif ($mode == 0) {
            if ($cline =~ /.*Serial Number: (\S+)/i) {
                ckserial;
                $crserial = lc($1);
                $crrev = "";
            } elsif ($cline =~ /.*Revocation Date: (.+)/i) {
                $crrev = $1;
            } 
        } elsif ($cline =~ /Signature Algorithm/) {
            last;
        }
    }
    ckserial;
}
if (-f $tempfile) {
    unlink ($tempfile);
}

$oktxt =~ s@\s+$@@;
print "$oktxt, still valid for $certdaysfmt days. ";
if ($crlskip == 0) {
    print "Serial $serial not found on any Certificate Revokation Lists.\n";
} else {
    print "CRL checks skipped, next check in " . ($crlupdatefreq - $cacheage) . " seconds.\n";
}

exit 0;