Fixing Weak Cipher Suites

Nessus Summary

Nessus ID: 26928

CVSS v3.0 Base Score: 5.3

Nessus Description:

The remote host supports the use of SSL ciphers that offer weak encryption.
Note: This is considerably easier to exploit if the attacker is on the same physical network.


How to Fix

This vulnerability is cased by a weak strength cipher being present in the SSL cipher suite. Weak strength is defined within Nessus as any cipher that is less than 64-bit. Fixing this is simple.

Apache Fix

The follow configuration should be added to the security.conf file to apply globally or to virtual host:

SSLCipherSuite EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH
SSLProtocol All -SSLv2 -SSLv3 -TLSv1 -TLSv1.1
SSLHonorCipherOrder On
SSLCompression off

IIS Fix

The Microsoft Knowledge Base article "How to Restrict the Use of Certain Cryptographic Algorithms and Protocols in Schannel.dll" describes how to enable just the FIPS 140 algorithms. Here's a summary:

Disable weak ciphers

Open the registry editor and locate HKLMSYSTEMCurrentControlSetControlSecurityProviders

Set "Enabled" dword to "0x0" for the following registry keys:

SCHANNELCiphersRC4 128/128
SCHANNELCiphersRC2 128/128
SCHANNELCiphersRC4 64/128
SCHANNELCiphersRC4 56/128
SCHANNELCiphersRC2 56/128
SCHANNELCiphersRC4 40/128
SCHANNELCiphersRC2 40/128
SCHANNELCiphersNULL
SCHANNELHashesMD5

Enable strong ciphers

Open the registry editor and locate HKLMSYSTEMCurrentControlSetControlSecurityProviders

Set "Enabled" dword to "0xffffffff" for the following registry keys

SCHANNELCiphersTriple DES 168/168
SCHANNELHashesSHA
SCHANNELKeyExchangeAlgorithmsPKCS

If the Enabled dword doesn't exist yet, please create the dword and set the value to "0x0" or "0xffffffff" as required.