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Tuesday, August 15, 2017

Birthday Attacks against TLS ciphers Used by OEM 13.2 Agent

Oracle Enterprise Manager 13.2 uses following cipher suites as default value for SSL communication,
 SSL_RSA_WITH_RC4_128_MD5, SSL_RSA_WITH_RC4_128_SHA and SSL_RSA_WITH_3DES_EDE_CBC_SHA
 
Which support ciphers as listed by script CipherScan.bsh (script details can be found at the end of this post),
[oracle@host01]$ ./CipherScan.bsh host01.dbaplus.ca:3872
 Following Cipher(s) is/are supported on server host01.dbaplus.ca:3872
     ECDHE-RSA-AES128-SHA256
     ECDHE-RSA-AES128-SHA
     DHE-RSA-AES128-SHA256
     DHE-RSA-AES128-SHA
     AES128-SHA256
     AES128-SHA
     DES-CBC3-SHA

Here, cipher DES-CBC3-SHA could introduce a security threat of 'Birthday Attack against TLS ciphers with 64bit block size vulnerability'. Remote attackers can obtain cleartext data via a birthday attack against a long-duration encrypted session of all versions of SSL/TLS protocol supporting cipher suites which use DES, 3DES, IDEA or RC2 as the symmetric encryption cipher in CBC mode.

It can be disabled/removed by configuring agent's properties. Before changing the agent property, one of following method can be used to check current setting,
* Run command: <AGENT_INST_HOME>/bin/emctl getproperty agent -name SSLCipherSuites or
* Check agent property file by running:  grep -i <AGENT_INST_HOME>/sysman/config/emd.properties
 
[oracle@host01]$ cd /u01/software/em/agent/agent_inst
[oracle@host01]$ ./bin/emctl getproperty agent -name SSLCipherSuites
Oracle Enterprise Manager Cloud Control 13c Release 2 
Copyright (c) 1996, 2016 Oracle Corporation.  All rights reserved.
SSLCipherSuites is unset; default value is SSL_RSA_WITH_RC4_128_MD5:SSL_RSA_WITH_RC4_128_SHA:SSL_RSA_WITH_3DES_EDE_CBC_SHA
[oracle@host01]$
[oracle@host01]$ grep -i 'SSLCipherSuites' ./sysman/config/emd.properties
[oracle@host01]$

The property is using default value and not set yet.
Remove weak cipher suite by setting SSLCipherSuites property of agent,
[oracle@host01]$ cd /u01/software/em/agent/agent_inst                      
[oracle@host01]$ ./bin/emctl setproperty agent -name SSLCipherSuites -value TLS_RSA_WITH_AES_128_CBC_SHA:TLS_RSA_WITH_AES_256_CBC_SHA:RSA_WITH_AES_256_CBC_SHA256
Oracle Enterprise Manager Cloud Control 13c Release 2 
Copyright (c) 1996, 2016 Oracle Corporation.  All rights reserved.
EMD setproperty succeeded

If the Agent is running on AIX platform, use the cipher SSL_RSA_WITH_AES_128_CBC_SHA only.
[oracle@host01]$ ./bin/emctl setproperty agent -name SSLCipherSuites -value SSL_RSA_WITH_AES_128_CBC_SHA


Check current value,
[oracle@host01]$ cd /u01/software/em/agent/agent_inst
[oracle@host01]$ ./bin/emctl getproperty agent -name SSLCipherSuites
Oracle Enterprise Manager Cloud Control 13c Release 2 
Copyright (c) 1996, 2016 Oracle Corporation.  All rights reserved.
SSLCipherSuites=TLS_RSA_WITH_AES_128_CBC_SHA:TLS_RSA_WITH_AES_256_CBC_SHA:RSA_WITH_AES_256_CBC_SHA256
[oracle@host01]$
[oracle@host01]$ grep -i ./sysman/config/'SSLCipherSuites' emd.properties
SSLCipherSuites=TLS_RSA_WITH_AES_128_CBC_SHA:TLS_RSA_WITH_AES_256_CBC_SHA:RSA_WITH_AES_256_CBC_SHA256
[oracle@host01]$

Restart agent,
[oracle@host01]$ /u01/software/em/agent/agent_13.2.0.0.0/bin/emctl stop agent
Oracle Enterprise Manager Cloud Control 13c Release 2
Copyright (c) 1996, 2016 Oracle Corporation.  All rights reserved.
Stopping agent ... stopped.
[oracle@host01]$
[oracle@host01]$ /u01/software/em/agent/agent_13.2.0.0.0/bin/emctl start agent
Oracle Enterprise Manager Cloud Control 13c Release 2
Copyright (c) 1996, 2016 Oracle Corporation.  All rights reserved.
Starting agent ............... started.


Verify the supported ciphers,
[oracle@host01]$ ./CipherScan.bsh host01.dbaplus.ca:3872
 Following Cipher(s) is/are supported on server host01.dbaplus.ca:3872
     AES128-SHA

There is no threat (weak cipher) any more.
 
Appendex.  Script file CipherScan.bsh
#!/usr/bin/bash
# -----------------------------------------------
# Scan available Cipher on given server with port
# Usage:
#    CipherScan.bsh  <SERVER_IP>:<PORT>
#
# For example,
#    ./CipherScan.bsh  host01.dbaplus.ca:3872
# -----------------------------------------------
SERVER=$1
CIPHER_SUPPORTED=$(openssl ciphers 'ALL:eNULL' | sed -e 's/:/ /g')
echo -e "\n Following Cipher(s) is/are supported on server $SERVER \n"
for cipher in ${CIPHER_SUPPORTED[@]}
do
    result=$(echo -n | openssl s_client -cipher "$cipher" -connect $SERVER 2>&1)
    if [[ "$result" =~ "Connection refused" ]] ; then
        echo  $result
        break
    fi
    if ! [[ "$result" =~ ":error:" ]] ; then
          echo "     "$cipher
    fi
done

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