A new OpenSSL vulnerability (CVE-2016-0800), called DROWN, was recently announced. It affects older versions of several widely used server technologies:
- SSLv2, an old version of the Secure Sockets Layer protocol. Most up‑to‑date websites don’t use Secure Sockets Layer (SSL) at all, having moved to Transport Layer Security TLS).
- IIS v7, an older version of Microsoft Internet Information Services
- NSS 3.13 (Network Security Services), a widely used cryptographic library
The DROWN vulnerability is described on a dedicated website, The DROWN Attack. DROWN stands for Decrypting RSA with Obsolete and Weakened eNcryption, and makes vulnerable websites susceptible to man‑in‑the‑middle attacks.
DROWN is unusual in that it does not require a site to actively use SSLv2 or other vulnerable protocols. A site is vulnerable if it supports one of the vulnerable protocols or shares a private key with any other server that allows SSLv2 connections.
Both NGINX Open Source and NGINX Plus support SSLv2, but it is turned off by default in all versions since NGINX 0.8.19 (released in October 2009). Only users who have explicitly turned on SSLv2, or use an NGINX version earlier than 0.8.19, or share a private key with another server that allows SSLv2 connections, are vulnerable to this attack.
Site owners should check whether their website configuration supports SSLv2 and disable it if it does. With NGINX and NGINX Plus, the use of SSL and TLS protocols is controlled by the
ssl_protocols configuration directive. In order to enable recent TLS only, and disable SSL v2 and SSL v3, use the following syntax:
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
Please see the reference documentation on SSL/TLS support with NGINX.
Visit the following sites for more information:
- The security advisory for DROWN from OpenSSL.org
- A detailed description of DROWN on ZDNet
- The DROWN Attack dedicated website
If you’re updating your NGINX configuration, or if you’re looking to improve application performance for your secure website, consider upgrading to HTTP/2. You can learn about the benefits in our recent HTTP/2 blog post and HTTP/2 white paper.
Image courtesy The Drown Attack.