SuperFish flashback: SSL interception bugs weaken Barracuda web filter

Barracuda Networks’ web filter is exposed to man-in-the-middle network attack due to a critical flaw in a feature used to inspect SSL traffic on corporate network.

The security appliance company on Tuesday warned customers not to use the SSL inspection feature without updating to firmware version for its Barracuda Web Filter.

The update fixes two bugs detailed in an advisory by the Department of Homeland Security sponsored CERT at Carnegie Mellon University on Tuesday, published as part of a coordinated disclosure with Barracuda.

The good news for Barracuda customers is that the company released update on nearly two weeks ago and says it has alerted customers to the “high” risk rated bug.

CERT said both flaws in the web filter’s SSL inspection feature “may allow an attacker to successfully achieve a man-in-the-middle (MITM) attack without the client knowing it.”

The first bug (CVE-2015-0961) affects Barracuda Web Filter version below fail to check upstream certificate validity when performing SSL inspection. The second bug (CVE-2015-0962) affects versions 7.0 through 8.1.003 and is due to the product shipping with one of three different default root CA certificates shared across multiple machines for use in the SSL inspection feature.

Barracuda discovered the two issues after conducting an audit, prompted by CERT’s earlier investigation into common errors in SSL inspection products. Barracuda’s product was one of nearly 60 that may contain security flaws, CERT said in March.

CERT vulnerability analyst Will Dormann ran the study following public furore over SuperFish adware that was pre-loaded on millions of Lenovo computers and employed similar methods to SSL inspection software.

SuperFish had annoyed users for displaying unwanted ads, but caused alarm after it was discovered the adware — which interfered with SSL encrypted web traffic — could introduce more security risks to users through flaws in its implementation. That came to a head after a security researcher extracted the private key SuperFish had used to intercept SSL traffic.

However, SuperFish was the tip of the iceberg, Dormann noted in March, explaining that SSL inspection software is fairly pervasive and used in everything from data loss prevention products to firewalls and secure web gateways.

Dormann outlined seven common mistakes in SSL inspection software that, like SuperFish, can raise new risks to users, largely due to a misunderstanding of the capabilities of SSL.

“SSL and TLS can practically achieve secure authentication and encryption only on a point-to-point basis, not an end-to-end basis,” he noted. In the latter case, an attacker may be standing between the client and the SSL interception software, yet there would be no way for the client of knowing the connection has been compromised.

But even if SSL inspection software didn’t contain those flaws, it still undermines the two main functions of of SSL, which is to vouch for the authenticity of a server and to encrypt data between a client and the server.

“The use of SSL inspection software reduces or completely prevents clients from successfully validating the identity of the servers that they are communicating with,” he noted.

“Given the architecture of SSL and TLS, users have a difficult enough time making a security decision based on the information provided to them. Once the concept of SSL inspection is thrown into the mix, it only makes the decision more difficult.”

This article is brought to you by Enex TestLab, content directors for CSO Australia.

Copyright © 2015 IDG Communications, Inc.

The 10 most powerful cybersecurity companies