Your antivirus and network protection efforts may actually be undermining network security, a new paper and subsequent US-CERT advisory have warned.

The issue comes with the use of HTTPS interception middleboxes and network monitoring products. They are extremely common and are used to check that nothing untoward is going on.

However, the very method by which these devices skirt the encryption on network traffic through protocols like SSL, and more recently TLS, is opening up the network to man-in-the-middle attacks.

In the paper [PDF], titled The Security Impact of HTTPS Interception, the researchers tested out a range of the most common TLS interception middleboxes and client-side interception software and found that the vast majority of them introduced security vulnerabilities.
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the user can only be sure that their connection to the interception product is legit, but has no idea whether the rest of the communication – to the web server, over the internet – is secure or has been compromised.

And, it turns out, many of those middleboxes and interception software suites do a poor job of security themselves. Many do not properly verify the certificate chain of the server before re-encrypting and forwarding client data. Some do a poor job forwarding certificate-chain verification errors, keeping users in the dark over a possible attack.

In other words: the effort to check that a security system is working undermines the very security it is supposed to be checking.

Source: Are you undermining your web security by checking on it with the wrong tools? • The Register