Vulnerability Note VU#583776

Network traffic encrypted using RSA-based SSL certificates over SSLv2 may be decrypted by the DROWN attack

Original Release date: 01 Mar 2016 | Last revised: 14 Mar 2016


Network traffic encrypted using an RSA-based SSL certificate may be decrypted if enough SSLv2 handshake data can be collected. This is known as the "DROWN" attack in the media.


According to the researcher, "DROWN" is a new form of cross-protocol Bleichenbacher padding oracle attack. An attacker using "DROWN" may obtain the session key from a vulnerable server supporting SSLv2 and use it to decrypt any traffic encrypted using the shared certificate.

It allows an attacker to decrypt intercepted TLS connections by making specially crafted connections to an SSLv2 server that uses the same private key."

The SSLv2 protocol is the only protocol directly impacted; however, the researcher's website states that many servers may use a shared certificate between the SSLv2 and the newer TLS protocols. If so, if the certificate is decrypted via SSLv2, then the TLS protocol using the shared certificate can be decrypted as well. The attack requires approximately 1000 SSL handshakes to be intercepted for the attack to be effective.

The researchers have also released a DROWN attack check tool and an FAQ that provides more complete information.


A remote attacker may be able to decrypt individual messages/sessions of a server supporting SSLv2. Servers using TLS protocol with the same shared certificate as is used for SSLv2 may also be vulnerable. According to the DROWN FAQ, the server private key is not obtained from this attack.


Disable SSLv2

Network administrators should disable SSLv2 support. The researchers have provided more information on how to disable SSLv2 for various server products.

SSLv2 has been deprecated since 2011.

Do not reuse SSL certificates or key material

This issue can be mitigated on TLS connections by using unique SSL keys and certificates. If possible, do not reuse key material or certificates between SSLv2 and TLS support on multiple servers.

Monitor network and use firewall rules

We recommend enabling firewall rules to block SSLv2 traffic. Since the attack requires approximately 1000 SSL handshakes, network administrators may also monitor logs to look for repeated connection attempts. However, this data may also be obtained via man-in-the-middle or other attacks, not solely from direct connections.

Vendor Information (Learn More)

On Linux, nginx may or may be affected depending on what version of OpenSSL nginx was compiled with. See the vendor list below or contact your vendor to determine if your release of nginx is affected.

VendorStatusDate NotifiedDate Updated
ECSystems.nlAffected-14 Mar 2016
OpenSSLAffected-02 Mar 2016
Apache-SSLUnknown-01 Mar 2016
CentOSUnknown-14 Mar 2016
Debian GNU/LinuxUnknown-14 Mar 2016
Microsoft CorporationUnknown-01 Mar 2016
MozillaUnknown-01 Mar 2016
nginxUnknown-14 Mar 2016
openSUSE projectUnknown-14 Mar 2016
PostfixUnknown-01 Mar 2016
Red Hat, Inc.Unknown-14 Mar 2016
SUSE LinuxUnknown-14 Mar 2016
UbuntuUnknown-14 Mar 2016
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base 7.1 AV:N/AC:H/Au:N/C:C/I:C/A:N
Temporal 6.1 E:POC/RL:W/RC:C
Environmental 6.5 CDP:ND/TD:H/CR:H/IR:H/AR:ND



Thanks to Nimrod Aviram for reporting this vulnerability.

This document was written by Garret Wassermann.

Other Information

  • CVE IDs: CVE-2016-0800
  • Date Public: 01 Mar 2016
  • Date First Published: 01 Mar 2016
  • Date Last Updated: 14 Mar 2016
  • Document Revision: 75


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