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CERTVU:583776

HistoryMar 01, 2016 - 12:00 a.m.

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

2016-03-0100:00:00

www.kb.cert.org

5.9 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

NONE

Availability Impact

NONE

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

4.3 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

NONE

Availability Impact

NONE

AV:N/AC:M/Au:N/C:P/I:N/A:N

0.952 High

EPSS

Percentile

99.3%

JSON

Overview

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.

Description

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.

Impact

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.

Solution

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

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.

583776

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ECSystems.nl __ Affected

Updated: March 14, 2016

Statement Date: March 10, 2016

Status

Affected

Vendor Statement

“Our version comes with a preferred cipher list which has mitigated SSLv2 issues since march 2015, our latest version 1.9.13.1 was released on 2 march 2016 with Openssl 1.0.2g which has the additional fix(es) for VU#583776.”

Vendor Information

ECSystems.nl supports NGINX for Windows

Vendor References

<http://nginx-win.ecsds.eu/>

OpenSSL __ Affected

Updated: March 02, 2016

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

OpenSSL 1.0.2g and 1.0.1s have been released to address this vulnerability. Please see OpenSSL’s security advisory at the URL below.

A 3rd-party tool <http://testssl.sh/> is available to check for security issues, including this one.

Another option for network administrators to determine if a server supports SSLv2 is to use the following command:

openssl s_client -connect host:443 -ssl2

If certificate information is returned, then SSLv2 is supported. It has been reported that this command may not work on Ubuntu or Debian systems.

Vendor References

<https://www.openssl.org/news/secadv/20160301.txt>

Addendum

nginx may or may be affected depending on what version of OpenSSL it was compiled with. Contact your vendor to determine if your release of nginx is affected.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%23583776 Feedback>).