EM12c OHS, LOW strength ciphers, custom certificates, and patch 19948000 weirdness

This post documents an unusual issue I encountered with the Oracle HTTP Server (OHS) installation in my Oracle Enterprise Manager 12c R4 ( environment after following MOS note 1984662.1 and applying patch 19948000 (CPUJAN2015) to my OHS home.  It also contains a workaround I found that you should consider UNSUPPORTED, UNOFFICIAL, and NOT RECOMMENDED, only for use if absolutely necessary to meet auditor requirements.  If you do not have to follow the steps I describe below, I suggest waiting for new patches and further guidance from Oracle Support. If this change breaks your system and eats all the food in the break room refrigerator, I warned you not to do it.

Like other security-conscious EM12c admins, I want to keep my installation secure, and so I watch closely when security patches become available for EM12c or its various components. Thus, when I noticed patch 19948000’s availability for OHS, which disables SSLv3, I installed it on my system, and confirmed through testing that OHS no longer permitted SSLv3 connections (test for yourself with: openssl s_client -connect host.domain.com:port -ssl3, or try my EM12c SSL security checkup script that I have blogged about previously).

As I proceeded with further hardening of my EM12c system, specifically an attempt to disable LOW and MEDIUM strength cipher suite usage as per MOS note 1477287.1, I noticed that after following the directions provided, all of my EM12c endpoints correctly rejected LOW and MEDIUM strength ciphers, with one exception.  The OMS HTTPS upload port, inexplicably, continued to permit LOW strength connections. It refused MEDIUM strength ciphers, but had no problem accepting a LOW strength DES-CBC-SHA connection over TLSv1:

$ openssl s_client -connect omshost.domain.com:4902 -cipher LOW
SSL handshake has read 4109 bytes and written 385 bytes
New, TLSv1/SSLv3, Cipher is DES-CBC-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
    Protocol  : TLSv1
    Cipher    : DES-CBC-SHA
    Session-ID: 37BF30668DCAD2CC5D0BAC4142CC1FA1
    Master-Key: [redacted]
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    Start Time: 1429290250
    Timeout   : 300 (sec)

This confused me greatly, as I had edited all configuration files as instructed, and none of my other OHS listen ports accepted this LOW strength cipher connection.  I spent quite a bit of time trying to diagnose and resolve the issue with no luck, until I eventually stumbled upon an odd fix.  If I remove or comment out the “IfDefine SSL” directives from my $GC_INSTANCE_HOME/WebTierIH1/config/OHS/ohs1/httpd_em.conf file, then suddenly OHS would refuse LOW strength cipher connections on this port, with no apparent ill effect on the other listening ports.

$ openssl s_client -connect omshost.domain.com:4902 -cipher LOW 
2282780:error:14077410:SSL routines:SSL23_GET_SERVER_HELLO:sslv3 alert handshake failure:s23_clnt.c:769:
no peer certificate available
No client certificate CA names sent
SSL handshake has read 7 bytes and written 67 bytes
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated

I have noted these IfDefine SSL directives with “HERE” in the excerpt below from my httpd_em.conf file.

## CAUTION: Edit only the .template version of this file!
##     The command
##         emctl secure [lock|unlock]
##     will replace httpd_em.conf (discarding your changes) 
##     using the httpd_em.conf.template file.
## This file contains virtual hosts and other directives
## required for the "Enterprise Manager Central Console"
## to function correctly.

#UseWebCacheIp On

<IfDefine SSL>      #### HERE
    Listen 4902
    <VirtualHost *:4902>
        <Location /empbs/upload>
            Order allow,deny
            Allow from all
        <Location /empbs/jobrecv>
            Order allow,deny
            Allow from all
        <Location /em>
            Order allow,deny
            Allow from all
        <Location /agent_download>
            Order allow,deny
            Allow from all
        <Location /xmlpserver>
            Order allow,deny
            Allow from all

        #DocumentRoot &ORACLE_HOME&/Apache/Apache/htdocs
        ServerName omshost.domain.com
        #Port 4902
        Timeout 900

        LogFormat "%h %l %u %t \"%r\" %>s %b [ecid: %{ECID-Context}i] [User-Agent: %{User-Agent}i]" common
        SetEnvIf Request_URI "\.(bmp|jpg|png|gif|css|js$)" no-log
        SetEnvIf Request_URI "/em/dynamicImage/*"  no-log
        CustomLog "|${ORACLE_HOME}/ohs/bin/odl_rotatelogs /oracle/oem/gc_inst1/WebTierIH1/diagnostics/logs/OHS/ohs1/em_upload_https_access_log 10M 100M" common env=!no-log

        ErrorLog "|${ORACLE_HOME}/ohs/bin/odl_rotatelogs /oracle/oem/gc_inst1/WebTierIH1/diagnostics/logs/OHS/ohs1/em_upload_https_error_log 10M 100M"
        SSLEngine on
        SSLCipherSuite HIGH
        SSLWallet file:/oracle/oem/gc_inst1/WebTierIH1/config/OHS/ohs1/keystores/upload
        SSLProtocol TLSv1

        <Files ~ "\.(cgi|shtml)$">
            SSLOptions +StdEnvVars
        #<Directory &ORACLE_HOME&/Apache/Apache/cgi-bin>
        #    SSLOptions +StdEnvVars
        SetEnvIf User-Agent ".*MSIE.*" nokeepalive ssl-unclean-shutdown
</IfDefine>     #### HERE
[remainder of file removed]

If I leave the IfDefine SSL statements in there, my OMS upload port accepts the weak DES-CBC-SHA cipher along with HIGH strength ciphers.  If I remove the IfDefine SSL, my OMS upload port refuses DES-CBC-SHA along with all other LOW/MEDIUM strength ciphers.

This makes no sense, given what I know of OHS and Apache-like products and the way that the handle the SSLCipherSuite configuration directive.

I raised this issue on Twitter and heard back from Andrew Bulloch at Oracle, who graciously spent quite a bit of time attempting to reproduce the issue on his side and working with me to identify the situations in which this behavior occurs.  After much testing, it appears that this behavior only occurs in the following situation:

  1. The OHS installed with EM12c R4 has patch 19948000 installed, AND
  2. The administrator has installed a third party SSL certificate, replacing the demo certificate used by default, AND
  3. The OHS httpd_em.conf contains the “IfDefine SSL” directive.

If I remove my custom certificate, returning the OMS to the demo certificate, the issue disappears, then returns if I reinstall the custom certificate.

If I remove patch 19948000, the issue disappears, and does not return whether I use a custom certificate or a demo certificate.

If I remove the IfDefine SSL directive, the issue disappears, and does not return whether I use a custom certificate, a demo certificate, or whether or not I have patch 19948000 installed.

I attempted to replicate this behavior with an SSL certificate that did not come from a true certificate authority, by using OpenSSL to create a CA, create a cert, sign it, then install it into OHS per the documentation in MOS note 1399293.1, but I could not reproduce it, possibly due to the fact that I used a certificate signed directly by a root CA (as with the demo certificate) instead of a certificate signed by an intermediate chain certificate signed by a root CA, as with the paid-for commercial certificate that revealed the issue. I have not had a chance to test that configuration.

Unfortunately, removing patch 19948000 means that OHS cannot refuse SSLv3 connections, and removing the custom certificate reverts the system back to the demo certificate that I do not wish to use, both of which will represent audit findings in regulated sites.

Due to this issue, I have edited my EM12c security checkup script to remove my recommendation to install patch 19948000, although I still have it installed.  For security reasons, I will leave my system in the workaround state I have described here, as I want SSLv3 disabled, and I want LOW strength cipher suites disabled, and I want to use a custom SSL certificate, but I accept the risk that I may have to undo this setup at any time to receive support or to successfully apply later patches.  You will have to make your own decisions based on your site’s audit requirements and the availability of personnel to validate your configuration and handle future patching.

I would be very interested if anyone else reading this has encountered this issue, as I do not know if my installation somehow uniquely surfaces this behavior or if the certificate vendor that we used has some strange settings on their certificates that cause confusion for OHS.


One thought on “EM12c OHS, LOW strength ciphers, custom certificates, and patch 19948000 weirdness

  1. Pingback: Securing Oracle Enterprise Manager 13c | Pardy DBA

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