The BEAST (Browser Exploit Against SSL/TLS) attack leverages weaknesses in CBC-mode cipher suites, allowing attackers to decrypt portions of encrypted traffic. While modern browsers have implemented client-side mitigations, server-side cipher prioritization remains important for defense-in-depth strategies.

Contrary to common expectation, Tomcat's ciphers attribute in server.xml doesn't enforce strict ordering. The Java JSSE layer makes the final selection based on:

• Key strength preferences
• JVM version and provider implementation
• Client capabilities during handshake

For Tomcat 6+, we can enforce cipher priority through JVM arguments in catalina.sh or catalina.bat:

export JAVA_OPTS="$JAVA_OPTS -Djdk.tls.ephemeralDHKeySize=2048"
export JAVA_OPTS="$JAVA_OPTS -Djdk.tls.server.cipherSuites=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384"

For granular control, create a custom SSLServerSocketFactory implementation:

public class PrioritizedCipherSSLSocketFactory extends SSLServerSocketFactory {
    @Override
    public String[] getDefaultCipherSuites() {
        return new String[] {
            "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
            "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
            "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
            // ... other prioritized ciphers
        };
    }
    // Implement remaining abstract methods
}

Configure it in server.xml:

<Connector 
    sslImplementationName="custom.PrioritizedCipherSSLSocketFactory"
    ... other attributes ...
/>

For systems using Tomcat's APR connector, modify OpenSSL configuration:

<Connector
    protocol="org.apache.coyote.http11.Http11AprProtocol"
    SSLEnabled="true"
    SSLCipherSuite="ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:!aNULL:!MD5:!DSS"
    SSLHonorCipherOrder="true"
/>

Use these tools to validate your configuration:

1. OpenSSL command: openssl s_client -connect yourdomain:443 -cipher ALL
2. SSL Labs test: https://www.ssllabs.com/ssltest/
3. TestSSLServer: java -jar TestSSLServer.jar yourdomain 443

Current best practices suggest:

• Disabling all CBC-mode ciphers in favor of AEAD modes (GCM)
• Enabling TLS 1.2+ exclusively
• Implementing certificate transparency
• Regular cipher suite rotation

The BEAST (Browser Exploit Against SSL/TLS) attack exploits a vulnerability in the CBC (Cipher Block Chaining) mode of operation in SSL/TLS. While modern browsers have implemented client-side fixes, server-side mitigation through cipher prioritization remains important for defense-in-depth strategies.

By default, Tomcat's JSSE implementation selects ciphers based on key strength rather than the order specified in server.xml. This behavior can be verified using tools like SSL Labs' SSL Test, which shows no cipher preference for default Tomcat configurations.

For the standard HTTP connector, you'll need to implement a custom SSLContext to enforce cipher priority. Here's a solution using a custom filter:

public class CipherPriorityFilter implements Filter {
    public void init(FilterConfig config) throws ServletException {
        String[] preferredCiphers = {
            "TLS_ECDHE_RSA_WITH_RC4_128_SHA",
            "TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
            // Add other ciphers in your preferred order
        };
        
        SSLContext context = SSLContext.getDefault();
        SSLEngine engine = context.createSSLEngine();
        engine.setEnabledCipherSuites(preferredCiphers);
    }
    // Other filter methods...
}

The APR connector offers more granular control through OpenSSL configuration. In your server.xml:

<Connector port="8443" protocol="org.apache.coyote.http11.Http11AprProtocol"
           SSLEnabled="true" 
           SSLCipherSuite="ECDHE-RSA-RC4-SHA:ECDHE-ECDSA-RC4-SHA:ECDH-RSA-RC4-SHA:ECDH-ECDSA-RC4-SHA:RSA-RC4-SHA:RSA-RC4-MD5:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK"
           SSLHonorCipherOrder="true" 
           ... />

While prioritizing RC4 was a common BEAST mitigation, modern recommendations suggest:

• Disabling RC4 completely due to newer vulnerabilities
• Using TLS 1.2+ with AEAD ciphers like AES-GCM
• Implementing perfect forward secrecy (PFS)

Here's a modern cipher suite configuration for Tomcat 8.5+:

sslEnabledProtocols="TLSv1.2"
ciphers="TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
         TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
         TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
         TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
         TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
         TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256"

Always test your configuration using:

• SSL Labs' SSL Test (https://www.ssllabs.com/ssltest/)
• OpenSSL command: openssl s_client -connect yourdomain:443 -cipher
• Java's built-in tools: jdk.tls.disabledAlgorithms in java.security file