The POODLE attack (SSLv3 with CBC cipher suites)
Description
The POODLE (Padding Oracle On Downgraded Legacy Encryption) vulnerability affects servers that support SSLv3 protocol with CBC-mode cipher suites. This flaw allows an attacker performing a man-in-the-middle (MITM) attack to decrypt sensitive data transmitted over SSL connections by exploiting weaknesses in SSLv3's padding validation. The attack is particularly dangerous because even servers that support modern TLS versions remain vulnerable if they allow fallback to SSLv3 for backward compatibility. Attackers can force protocol downgrade and then exploit the padding oracle to extract plaintext data, such as session cookies or authentication tokens, through repeated connection attempts.
Remediation
Immediately disable SSLv3 protocol support on all servers and ensure only TLS 1.2 or higher is enabled. Follow these configuration steps for common web servers:
For Apache:
Add or modify the SSLProtocol directive in your SSL configuration:
SSLProtocol all -SSLv2 -SSLv3 SSLCipherSuite HIGH:!aNULL:!MD5:!3DES
For Nginx:
Update the ssl_protocols directive to exclude SSLv3:
ssl_protocols TLSv1.2 TLSv1.3; ssl_ciphers HIGH:!aNULL:!MD5:!3DES;
For IIS:
Disable SSLv3 via registry or use IIS Crypto tool to configure protocols.
After making changes, restart the web server and verify the configuration using SSL testing tools such as SSL Labs' SSL Server Test. Additionally, ensure client applications do not attempt SSLv3 fallback by disabling legacy protocol support in client configurations.