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The kind folk at shared a new @zoom_us security issue with me.

I want to take this opportunity to describe:

The issue

How Zoom et al should fix it

How purchasers should identify it before corporate purchasing

What individuals should do

Zoom has been in the news for security issues a lot lately.

I’m choosing to share this info because Zoom has been very good in responding to security researchers and security problems.

It is apparent they care now... but how bad is their security deficit?

Let’s quantify

To avoid adding to the FUD let me state this up front:

If you use Zoom at home for personal reasons to remain connected to loved ones during the pandemic - that’s very important.

You should probably continue using the product.

Hopefully Zoom will update and improve.

CITL took a look at the Linux Zoom software and frankly it is surprisingly security deficient. I mean *surprisingly* deficient!

@m0thran did the analysis I’m about to share. (You should follow him)

Let’s quantify the issue and then show what to do about it.

The Linux Zoom binary is 42M (!), is at /opt/zoom/zoom, and version is 3.5.383291.0407.

It lacks so many base security mitigations it would not be allowed as a target in many Capture The Flag contests.

Linux Zoom would be considered too easy to exploit!

How do we know?

CITL uses their own software tools that aren’t open source (yet), you can find free software with a subset of their checks.

The Linux checksec shell script works fine for this.

Notice the binary lacks DEP/ASLR/Canaries/Fortification/RO section orders

[ @wdormann image]

The absence of these basic security and safety attributes make make the application exceedingly easy to exploit. I’ll show coding vulnerabilities in a bit).

Disabling all of them is impressive.

Perhaps Zoom using a 5 year out of date development environment helps (2015).

It’s not hard to find vulnerable coding in the product either.

Here’s an example of grabbing an untrusted environment variable and handing it to the insecure popen(3) function for execution [ @m0thran ]

There are plenty of secure-coding-101 flaws here.

The best time to engage in secure coding practices and development hygiene is at the start of the project.

The next best time is NOW!

So what can Zoom, and other companies, do to avoid these problems?

Treat Secure Development like any other component of your DevOps routines:

For compiler/linker/loader security:

Create unit tests!

Add them to the build cycle!

No builds ship if basic safety mitigations are lacking, were removed, or are insufficient.

Heck, use checksec

Keep your compiler tool chain up to date. A lot of security improvements have been put into compilers over the years.

With up to date toolchains and safety measures enabled, put those unit tests are in place.

Not doing this is irresponsible.

What about unsafe functions?

Microsoft figured out a way to tackle unsafe functions: they maintain a blacklist of functions that are difficult to use safely and easy to use unsafely.

Code is scanned during build and the build fails if unsafe function calls are found.

Basic development hygiene. Do it.

Want a prebuilt list of risky library functions?

Pull them from MSFT (anything with a *_s replacement)

or GCC/Clang Source Fortification ( all with *_chk replacement)

or any number of books in writing secure code ( The Art of Security Assessment or CERT’s Secure Code )

Even with compiler enabled Source Code Fortification, have your unit tests evaluate the resultant binary.

Check that weak functions were replaced (systemd is an example of failures here).

Better: to begin with avoid risky functions if possible.

The Linux Zoom application demonstrates a surprising lack of security, but this isn’t all on Zoom.

In fact I think Zoom will start turning this around due to the external focus.

Companies consuming/purchasing this specific software are at fault to.

What can they do?...

It can be as simple as running the same checks that should be present as unit tests in the build process.

If the software is missing basic security artifacts, it’s unlikely the company considers the security of their product.

Look for competitor products.

It could be a quick evaluation of Zoom Linux software played a roll in Google banning the software.

Google has a large number of Linux client systems.

Exceedingly week security on those systems that processes data from outside of Google is a valid risk.

If so, valid call

/17 will release their tools for Linux, Windows, OSX and a range of hardware architectures, however CITL’s software is overkill for this.

Plenty of free solutions for the basics:………

Back to the average user.

That’s not Linux.

It’s not an urgent threat model... yet. If folks rush to exploit this soft target that could change.

The Windows and Mac clients aren’t “quite” as bad. Likely because Zoom unintentionally used more recent dev toolchains.

Are there alternatives? In some cases sure.

If these alternatives are your company’s product, where are your security unit tests?!?

If you are a corporate consumer you should include simple security metrics in your product evaluation and purchasing process.


The popen() example was meant as an example of identifying poor security coding practices.

There are 453 calls to bad security funcs (unbounded string copies, bad random, access(), ...)

6316 to risky funcs like popen

Feel free to choose a more exploitable example :)
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