Security Bulletin: Vulnerability in RC4 stream cipher affects Rational Developer for System z (CVE-2015-2808)

Summary

The RC4 “Bar Mitzvah” Attack for SSL/TLS affects Rational Developer for System z.

Vulnerability Details

CVEID: CVE-2015-2808**
DESCRIPTION:** The RC4 algorithm, as used in the TLS protocol and SSL protocol, could allow a remote attacker to obtain sensitive information. An attacker could exploit this vulnerability to remotely expose account credentials without requiring an active man-in-the-middle session. Successful exploitation could allow an attacker to retrieve credit card data or other sensitive information. This vulnerability is commonly referred to as “Bar Mitzvah Attack”.
CVSS Base Score: 5
CVSS Temporal Score: See <https://exchange.xforce.ibmcloud.com/vulnerabilities/101851&gt; for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (AV:N/AC:L/Au:N/C:P/I:N/A:N)

Affected Products and Versions

Rational Developer for System z, versions 8.0.3.x, 8.5.x, 9.0.x and 9.1.x

Workarounds and Mitigations

By default Rational Developer for System z relies on System SSL defaults for active cipher suites, and by default, System SSL enables the RC4 cipher suites for SSLv3 and all TLS versions. Note that usage of SSLv3 is not advised due to another vulnerability commonly referred to as “POODLE vulnerability”.

The RC4 ciphers in TLS are:

• TLS_RSA_WITH_RC4_40_MD5 (“03” or “0003”)
• TLS_RSA_WITH_RC4_128_MD5 (“04” or “0004”)
• TLS_RSA_WITH_RC4_128_MD5 (“05” or “0005”)
• TLS_ECDH_ECDSA_WITH_RC4_128_SHA (“C002”)
• TLS_ECDHE_ECDSA_WITH_RC4_128_SHA (“C007”)
• TLS_ECDH_RSA_WITH_RC4_128_SHA (“C00C”)
• TLS_ECDHE_RSA_WITH_RC4_128_SHA (“C011”)

You can explicitly disable the usage of the RC4 ciphers by adding the GSK_V3_CIPHER_SPECS environment variable, ensuring that the environment variable character string does not include ciphers “03”, “04”, or “05”.
If environment variable GSK_V3_CIPHERS is set to GSK_V3_CIPHERS_CHAR4 (this must be done explicitly), you can explicitly disable the usage of the RC4 ciphers by adding the GSK_V3_CIPHER_SPECS_EXPANDED environment variable, ensuring that the environment variable character string does not include ciphers “0003”, “0004”, “0005”, “C002”, “C007”, “C00C”, or “C011”.

Rational Developer for System z has two components that utilize System SSL:

• RSE, which is used when a client connects to the host. You must specify the GSK_V3_CIPHER_SPECS environment variable in rsed.envvars, by default located in /etc/rdz.
• Debug Manager, by means of an AT-TLS policy. You must create a file holding the GSK_V3_CIPHER_SPECS environment variable and reference it via the Envfile keyword in the TTLSGroupAdvancedParms section.

You should verify applying this configuration change does not cause any compatibility issues. Not disabling the RC4 stream cipher 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 RC4 stream cipher and take appropriate mitigation and remediation actions.