Fixing SSL RC4 Cipher Suites Supported (Bar Mitzvah)

Fixing SSL RC4 Cipher Suites Supported (Bar Mitzvah)

Posted by Peter Bassill on 01/01/2015


Nessus Summary



Nessus ID: 65821



CVSS v3.0 Base Score: 2.6



Nessus Description:



The remote host supports the use of RC4 in one or more cipher suites. The RC4 cipher is flawed in its generation of a pseudo-random stream of bytes so that a wide variety of small biases are introduced into the stream, decreasing its randomness. If plaintext is repeatedly encrypted (e.g., HTTP cookies), and an attacker is able to obtain many (i.e., tens of millions) ciphertexts, the attacker may be able to derive the plaintext.



How to Fix



This vulnerability is cased by a RC4 cipher suite present in the SSL cipher suite. Fixing this is simple.



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

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