The OpenSSL “CVE-2015-1793” certificate verification bug


hearbleed-sslIf you have anything to do with web security, like we do, you’ve probably been in “bated breath” mode this week.

That’s because the OpenSSL team announced, on Monday 2015-07-06, that it had a “high severity” update coming out in three days’ time, meaning today, Thursday 2015-07-09:

The OpenSSL project team would like to announce the forthcoming release of OpenSSL versions 1.0.2d and 1.0.1p.

These releases will be made available on 9th July. They will fix a single security defect classified as "high" severity. This defect does not affect the 1.0.0 or 0.9.8 releases.

And that’s all she wrote.

What is OpenSSL?

OpenSSL is a very widely used internet security toolkit that implements a cryptographic security protocol called TLS/SSL, and puts the “S” in HTTPS for a great many websites.

OpenSSL is also widely known because of the Heartbleed vulnerability, uncovered in 2014.

Heartbleed meant that almost anyone with an internet connection could suck secret data out of your servers at will, without actually needing to break in or even to do any sort of hacking.

To trigger the Heartbleed bug, you merely asked the server to send you a so-called keep-alive message.

A keep-alive system is an uncontroversial feature that many internet protocols support, because keeping an existing connection going is a lot less complicated than starting a new one.

Keep-alives are a bit like those short conversations about not very much that you have every now and then when you’re travelling in a car at night, just to make sure the driver’s still alert.

The Heartbleed problem was that you could ask the server to send you a keep-alive response that was much larger than the memory buffer it was using to process your keep-alive message, and it would happily oblige.

So, you’d receive a reply that included your message, followed by random extra stuff out of server memory that you weren’t supposed to see.

Most of it would be harmless, but every now and then you might get hold of snippets of other people’s traffic, passwords, encryption keys, and more.

Waiting for the fix

These historical facts – the prevalence of OpenSSL and bad memories of Heartbleed – meant that OpenSSL’s terse email notification on Monday wasn’t very comforting.

Why an update just for a single security hole? How “high” was the high severity?

Was this going to be a denial-of-service bug? Or would it be a data leakage hole, like Heartbleed?

Or a full-on remote code execution flaw that would allow outsiders to run commands on your server as if they were actually logged in to your network?

More specifically, would all sub-versions of OpenSSL in the 1.0.1 and 1.0.2 series be at risk, or would some releases turn out to be OK?

How to prepare for what was coming on Thursday?

The flaw


The update is out, and our verdict is that the bug isn’t as bad or as widespread as we feared at first.

Nevertheless, if you’re vulnerable, you need to act.

Simply explained, CVE-2015-1793 is a certificate verification flaw.

This means that crooks who can lure or misdirect you to a bogus website (or email server, or indeed any internet service using TLS/SSL for its security) may be able trick you into thinking that you are somewhere legitimate and secure.

As you probably know, TLS/SSL relies on a “chain of trust” formed by cryptographic certificates.

This chain of certificates reassures you that the secure website you are visiting really does belong to the organisation you expect.


Author: Amanda Walker

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