Secure Client-Initiated SSL Renegotiation

The negotiation process of the SSL encryption uses much more resources on the server than on the client. If the client can initiate the renegotiation process, an attacker can render the server unavailable with a Denial of Service attack.

Security Assessment

CVSS Vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Vulnerability Information

The negotiation process of the SSL encryption uses significantly more resources on the server than on the client. If the client can initiate the renegotiation process, an attacker can render the server unavailable with a Denial of Service attack.

Guides

This problem has been fixed in recent webserver versions. E.g. the latest versions of Apache and nginx do not allow client initiated SSL renegotiation. Therefore make sure that your webserver is up-to-date.

E.g. run:

https://github.com/crashtest-security/gist/blob/master/ssl_tls_vulnerabilities/secure_ssl_renegotiation

For more information about Crashtest Security visit crashtest-security.com.