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OpenSSL project published a security advisory yesterday (5th June 2014) providing information on a SSL/TLS Man-In-The-Middle vulnerability. By sending a special sequence of carefully crafted SSL packets to vulnerable client and server, an attacker posing as the Man-in-the-Middle can decrypt and eavesdrop/modify the traffic between the client and the server.
SSL/TLS also called Secure Socket Layer protocol/Transport Layer Security protocol is used predominantly in the Internet to encrypt the traffic between a client and a server. For e.g. the traffic between your browser and your financial organization (such as banks etc.) is encrypted using the SSL/TLS protocols. The OpenSSL project provides an open source toolkit to implement the SSL/TLS protocol. This toolkit is very widely used on a number of servers and also clients that communicate with the servers on the internet.
The following versions of OpenSSL are affected by this vulnerability:
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OpenSSL 1.0.1 through 1.0.1g
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OpenSSL 1.0.0 through 1.0.0l
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all versions before OpenSSL 0.9.8y
It is advised to upgrade to the following or any later versions:
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OpenSSL 1.0.1h
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OpenSSL 1.0.0m
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OpenSSL 0.9.8za
As part of the SSL/TLS protocol, during the setup of an encrypted communication channel between the client and the server, the client and server exchange information in a particular sequence.
Some of the important items exchanged during the setup of the encrypted channel are:
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Client and Server negotiated encryption algorithm
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Client random number
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Server random number
Using the above, the client computes a pre-master key and sends it to the server. Both sides use the pre-master key to generate the master key which is then used to generate a session-key. Both sides then indicate that they will subsequently use the session-key for encrypting the communication by sending a “ChangeCipherSpec” message.
In order to exploit this vulnerability, an attacker acting as the man-in-the-middle can send this “ChangeCipherSpec” message to both client and server prior to the client sending the pre-master key. This causes a vulnerable version of OpenSSL to assume that the pre-master is zero length and to go ahead with the generation of the master key and the subsequent session-keys. The attacker himself can also generate the same master key/session-keys and hence can decrypt/modify the communication between the client and the server.
An important prerequisite to launch a successful exploit against this vulnerability is to have both a vulnerable OpenSSL Client and also a vulnerable OpenSSL Server.
Typical man-in-the-middle attacks are difficult to achieve but given today’s adoption of public or rogue wifi hotspots/networks they are easy to execute. Given such scenarios it becomes important to protect ourselves against exploits taking advantage of this vulnerability.
Modern web browsers do not typically use OpenSSL. Hence, consumers using browsers to access Cloud Apps are not impacted by this vulnerability. At the same time, if native applications such as an iOS apps or Android apps are being used, it is important to ascertain from the Cloud App vendor if vulnerable version of OpenSSL is used. If vulnerable version is used, consumers should upgrade to the patched version as and when the Cloud App vendor publishes an updated app.
As a Cloud App vendor it is important to ensure that all the servers using vulnerable OpenSSL are patched against this vulnerability.
It is also important to assess as an enterprise if any appliances such as VPN, Proxies, etc. are using vulnerable versions of OpenSSL. Please contact the respective vendors for the applicable patches/upgrades. In case of any custom clients/servers created by your enterprise, please upgrade them with the latest OpenSSL toolkits.
At Netskope, our cloud security research team is continuously monitoring the Cloud App vendor servers and will update this space with specific information.
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