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Security Bulletin: Vulnerability in Diffie-Hellman ciphers affects IBM® WebSphere Real Time (CVE-2015-4000)

Security Bulletin


The Logjam Attack on TLS connections using the Diffie-Hellman (DH) key exchange protocol affects IBM® WebSphere Real Time

Vulnerability Details

CVEID: CVE-2015-4000
 The TLS protocol could allow a remote attacker to obtain sensitive information, caused by the failure to properly convey a DHE_EXPORT ciphersuite choice. An attacker could exploit this vulnerability using man-in-the-middle techniques to force a downgrade to 512-bit export-grade cipher. Successful exploitation could allow an attacker to recover the session key as well as modify the contents of the traffic. This vulnerability is commonly referred to as "Logjam".
CVSS Base Score: 4.3
CVSS Temporal Score: See for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (AV:N/AC:M/Au:N/C:P/I:N/A:N)

Affected Products and Versions

This vulnerability affects IBM WebSphere Real Time Version 3 Service Refresh 9 and earlier releases


The fix for this vulnerability is included in IBM WebSphere Real Time Version 3 Service Refresh 9 Fix Pack 1 and subsequent releases.

IBM customers should download WebSphere Real Time updates from Fix Central.

IBM WebSphere Real Time releases can also be downloaded from developerWorks.

The APAR for this fix is IV73934.

Further information on the changes associated with this vulnerability can be found here.

As the length of the server key size are increased, the amount of CPU required for full TLS/SSL handshake can significantly increase. Please carefully test and assess the impact to your CPU requirements to ensure sufficient CPU resources, otherwise the system availability may be impacted.

Workarounds and Mitigations

The vulnerability can be mitigated by explicitly disabling DH and DHE ciphers, using one of the following options:

  • Disable DH and DHE cipher suites by adding the DH and DHE cipher suites to the list of disabled algorithms defined by the jdk.tls.disabledAlgorithms security property in file.
  • Ensure that the DH or DHE cipher suite(s) are not explicitly enabled via the setEnabledCipherSuites() method.
  • If using the API, set the https.cipherSuites system property so that it does not include DH or DHE cipher suites.
  • Configure SP800-131a strict compliance or any Suite B configuration.

You should verify applying this configuration change does not cause any compatibility issues. If you change the default setting after applying the fix, you will expose yourself to the attack described above. IBM recommends that you review your entire environment to identify other areas where you have enabled the Diffie-Hellman key-exchange protocol used in TLS and take appropriate mitigation and remediation actions.

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Reported to IBM by The WeakDH team at

Change History

19 June 2015: Original version published
1 July 2015: Minor improvement in Remediation/Fixes section

*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.


According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY.

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Document Information

Modified date:
15 June 2018