CVE-2016-2183 – SSL/TLS remediation

CVE-2016-2183: SSL/TLS: Report Vulnerable Cipher Suites for HTTPS

Overview

CVE-2016-2183, commonly referred to as the SWEET32 vulnerability, is a flaw affecting SSL/TLS protocols using certain 64-bit block cipher suites, particularly 3DES (Triple Data Encryption Standard) and Blowfish. This vulnerability, discovered in 2016, targets HTTPS services that utilize these older ciphers, which are susceptible to attacks due to their smaller block sizes.

SWEET32 exploits weaknesses in block cipher modes with a 64-bit block size, allowing an attacker to decrypt certain portions of encrypted data under specific circumstances. This vulnerability is especially concerning in long-lived HTTPS sessions, where sufficient data can be captured to execute a successful attack.

Vulnerability Details

1. Vulnerability Mechanism: SWEET32 takes advantage of the way 64-bit block ciphers operate in block cipher modes. In these modes, every 64-bit block of plaintext is encrypted independently, leading to a risk of “birthday attacks.” When a substantial amount of data is encrypted with the same key (often several gigabytes), the probability of block collisions increases, and repeated blocks can reveal patterns that expose portions of sensitive information.
2. Affected Cipher Suites:
   • SSL/TLS configurations that use 3DES and Blowfish as encryption algorithms are vulnerable, especially in configurations where they are used for HTTPS traffic over long-lived sessions.
   • 3DES (Triple DES): Typically employed in legacy systems, 3DES is vulnerable due to its smaller block size of 64 bits, which is no longer considered sufficient for modern encryption needs.
   • Blowfish: Another 64-bit block cipher, Blowfish is similarly vulnerable, although less frequently used in HTTPS configurations.

Impact and Risks

The primary risk of CVE-2016-2183 is the potential for an attacker to capture network traffic and analyze it to retrieve sensitive information. This vulnerability does not immediately compromise all data, but over time and with significant data capture, it allows attackers to deduce parts of the encrypted data through block collision analysis.

• Information Disclosure: Attackers can potentially access confidential information within encrypted data streams.
• Session Integrity: Compromised data could reveal user sessions, credentials, or other private information in HTTPS transactions.

Mitigation and Remediation

To address CVE-2016-2183, the best practice is to disable 64-bit block ciphers in SSL/TLS configurations and shift to more modern, secure algorithms.

1. Disable Vulnerable Ciphers:
   • Update server configurations to remove 3DES and Blowfish from the list of supported ciphers.
     • Computer Configuration > Administrative Templates > Network > SSL Configuration Settings
       • In SSL Cipher Suite Order, enable policy if it is not enable
       • Delete:
         • TLS_RSA_WITH_3DES_EDE_CBC_SHA
         • TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA
     • Quit Group Policy and restart server.
     • Using PowerShell
       • Get-TlsCipherSuite -Name DES
       • Disable-TlsCipherSuite -Name TLS_RSA_WITH_3DES_EDE_CBC_SHA
       • Get-TlsCipherSuite -Name DES to verify
   • Configure the server to prioritize 128-bit or 256-bit ciphers like AES (Advanced Encryption Standard), which uses a larger block size and is resistant to SWEET32.
2. Update TLS/SSL Protocols:
   • Ensure servers support newer versions of TLS (1.2 or 1.3), which have more secure cipher suite selections by default.
   • Older versions, including SSL and early TLS, should be phased out as they support outdated and insecure ciphers.
3. Regularly Patch and Update:
   • Regularly update SSL/TLS libraries and server software to the latest versions, ensuring they apply the latest security fixes and optimizations.

Conclusion

CVE-2016-2183 (SWEET32) highlights the importance of continuously evaluating cryptographic protocols and configurations. While 3DES and Blowfish were once reliable encryption methods, they no longer provide adequate security in today’s data-intensive environments. By disabling vulnerable ciphers and adopting modern encryption standards, organizations can protect data integrity, enhance user privacy, and secure communication channels from potential threats.

Reference:

NIST

How do I fix CVE-2016-2183