Security Bulletin: Vulnerability in Diffie-Hellman ciphers affects IBM® SDK, Java™ Technology Edition (CVE-2015-4000)

Summary

The Logjam Attack on TLS connections using the Diffie-Hellman (DH) key exchange protocol affects IBM SDK, Java Technology Edition.

Vulnerability Details

CVEID: CVE-2015-4000**
DESCRIPTION:** 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 https://exchange.xforce.ibmcloud.com/vulnerabilities/103294 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

These vulnerabilities affect IBM SDK, Java 2 Technology Edition, Version 5.0 Service Refresh 16 Fix Pack 10 and earlier releases
These vulnerabilities affect IBM SDK, Java Technology Edition, Version 6 Service Refresh 16 Fix Pack 4 and earlier releases
These vulnerabilities affect IBM SDK, Java Technology Edition, Version 6R1 Service Refresh 8 Fix Pack 4 and earlier releases
These vulnerabilities affect IBM SDK, Java Technology Edition, Version 7 Service Refresh 9 and earlier releases
These vulnerabilities affect IBM SDK, Java Technology Edition, Version 7R1 Service Refresh 3 and earlier releases
These vulnerabilities affect IBM SDK, Java Technology Edition, Version 8 Service Refresh 1 and earlier releases

Remediation/Fixes

The fixes for these vulnerabilities are included in IBM SDK, Java 2 Technology Edition, Version 5.0 Service Refresh 16 Fix Pack 11 and earlier releases
The fixes for these vulnerabilities are included in IBM SDK, Java Technology Edition, Version 6 Service Refresh 16 Fix Pack 5 and subsequent releases
The fixes for these vulnerabilities are included in IBM SDK, Java Technology Edition, Version 6R1 Service Refresh 8 Fix Pack 5 and subsequent releases
The fixes for these vulnerabilities are included in IBM SDK, Java Technology Edition, Version 7 Service Refresh 9 Fix Pack 1 and subsequent releases
The fixes for these vulnerabilities are included in IBM SDK, Java Technology Edition, Version 7R1 Service Refresh 3 Fix Pack 1 and subsequent releases
The fixes for these vulnerabilities are included in IBM SDK, Java Technology Edition, Version 8 Service Refresh 1 Fix Pack 1 and subsequent releases

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.

IBM SDK, Java Technology Edition releases can be downloaded, subject to the terms of the developerWorks license, from here

IBM customers requiring an update for an SDK shipped with an IBM product should contact IBM support, and/or refer to the appropriate product security bulletin.

The APAR for this fix is IV73934.

Workarounds and Mitigations

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

IBM SDK, Java Technology Edition, Version 7**, 7R1 and 8 only**

• 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 java.security file.

AllIBM SDK, Java Technology Edition versions

• Ensure that the DH or DHE cipher suite(s) are not explicitly enabled via the setEnabledCipherSuites() method.
• If using the javax.net.ssl.HttpsURLConnection 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.