Weak Cipher Suites Appear in Security Scans
Weak Ciphers Appear in Vulnerability Scans
Security Vulnerability scanning software may generate a list of cipher suites you would like to deactivate. The command:
zmprov mcf +zimbraSSLExcludeCipherSuites <cipher_suite_name>
may be used to exclude these weak ciphers. However, the names of the ciphers listed in the vulnerability scan may be in OpenSSL format, and not match the name for the cipher suite that Zimbra's Jetty server uses.
See here for a list of cipher suites used by Zimbra's Java JSSE implementation:
The following link maps the SSL or TLS cipher suite names from the relevant specification to their OpenSSL equivalents:
Be sure to use the SSL or TLS specification names from the above Java documentation when invoking the zimbraSSLExcludeCipherSuites parameter.
For example: zmprov mcf +zimbraSSLExcludeCipherSuites SSL_RSA_EXPORT_WITH_RC2_CBC_40_MD5
would be used if you are given the OpenSSL format "EXP-RC2-CBC-MD5" by the scanning software.
Another source for weak ciphers in a scan is Postfix on Port 25. Please see here for info on disabling weak ciphers for Postfix:
Nginx Ciphers If you are using a Proxy you should check the SSL ciphers used there as well:
zmprov gacf zimbraReverseProxySSLCiphers
This command should remove the weak ciphers we have seen in recent security scans, although more may appear in the future. Please note the syntax and the format for the cipher list. You may add additional cipher suites to this list as needed. Make sure to use "\" to escape the "!" character so that the shell is not confused by it.
zmprov mcf zimbraReverseProxySSLCiphers \!DHE-RSA-AES256-SHA:\!ADH:\!SSLv2:\!MD5:HIGH