What Is The DROWN Attack/Vulnerability & Should I Be Worried?

DROWN is a new way to exploit vulnerabilities in SSLv2 to decrypt stolen information being communicated on an intercepted connection between users and servers. If you want a technical deep-dive on how it works, visit www.drownattack.com.

Who is vulnerable to the DROWN attack?

Any service that depends on TLS could be vulnerable. Websites and mail servers are likely the bulk of this category. Any server that allows SSLv2 connections, or uses the same private key as another server that allows SSLv2 connections, is potentially vulnerable.

It is important to note that even if you don't make a habit of using SSLv2 (which you shouldn't since it is wildly insecure), even just allowing some of your servers to support SSLv2 connections now makes them insecure.

The researchers who revealed the vulnerability this morning claim that up to 33% of HTTP servers worldwide are vulnerable.

Am I Affected!?

Do any of your servers allow SSLv2 connections? If so, you could be vulnerable. This is true even if you don't use SSLv2. All the vulnerability requires is for one of your machines to allow this type of connection.

What do I do?

Turn off SSLv2 support as soon as possible, and monitor your system to see whether a suspiciously high number of SSLv2 connection attempts has occurred. The attack involves using SSLv2 connections to get the target server to leak information about the private keys used. According to the researchers, about 40,000 SSLv2 probe connections are required to get the information needed to decrypt one out of 900 stronger TLS connections.

How can I tell if my servers have been probed with SSLv2 connections?

I'm glad you asked. ExtraHop's Cipher Suite & Encryption monitoring capabilities do just that. By analyzing all the data flowing across your network, ExtraHop can show you the number of SSLv2 and SSLv3 connections to devices, as well as other vital security info, like when your certificates are expiring, and where suspicious connections have originated.

A screenshot showing ExtraHop's view of insecure SSL versions in use on a network, as well as upcoming certificate expirations.

More Resources for learning about the DROWN vulnerability?

• The full research paper where the researchers first published this vulnerability is available here: https://drownattack.com/drown-attack-paper.pdf.
• Dan Goodin at ArsTechnica did a great writeup of the situation.
• There's some excellent discussion of the DROWN vulnerability, and the weakness of SSLv2, TLS, RSA, and other security technologies over on Hacker News.