Decrypting TLS Browser Traffic with Wireshark

https://jimshaver.net/2015/02/11/decrypting-tls-browser-traffic-with-wireshark-the-easy-way/

132 37 11 years ago

theatraine2• 11 years ago

This is handy, but you can very easily do this automatically with fiddler. It automatically swaps out all of the certs though.

gear54rus2• 11 years ago

Do you mean using Fiddler (great program, definitely a musthave) in place of Wireshark?

In that case you can add its key to a trusted authorities in Firefox and then it swaps nothing, everything seems to be signed properly... Unless I misunderstood your comment.

theatraine2• 11 years ago

I meant that Fiddler switches the original certificates with certificates that it generates. It's not a big deal if you trust them (on Windows Chrome and IE work automatically since it adds them to the trusted root store) and for Firefox you just have to trust the Fiddler issued certificate. However, if you inspect the certificate of an HTTPS site when Fiddler is running you see the CA is "DO_NOT_TRUST_FiddlerRoot".

throwaway8384• 11 years ago

No, Fiddler is an active ManInTheMiddle attack. With HTTPS interception it always substitutes the certificate (which is the public key).

The substituted public key allows the proxy to negotiate a TLS session between the browser and the proxy, impersonating the real server.

You avoid a certificate error if you install the signing CA certificate in the browser; but you still tamper with the traffic. There are scenarios where mitm doesn't work; for example Client Authenticated TLS. Things like certificate pinning, where the browser expects a specific public key, also break intetception.

charlesnw• 11 years ago

Spaces. Use them. I read "musthave" as "mutshave" :)

teh_klev• 11 years ago

Sure, but if you want to see the whole stack (below HTTP/S) you can't do that with fiddler.

mobiplayer2• 11 years ago

I find httpWatch with Firefox and IE much better than Fiddler for HTTP debugging purposes. However it is not free.

lucb1e• 11 years ago

I can't help but wonder how many people are going to apply this handy trick to people's unlocked Windows sessions...

bigiain2• 11 years ago

I'm looking forward with interest to see how long it takes for a piece of malware to start reconfiguring exploited machine's browsers and exfiltrating session keys.

(Or, to the news that the NSA/GHCQ/ASIO/et al. have been actively doing this for years already...)

skolor• 11 years ago

Have we seen malware ripping keys out of memory? It seems a stretch to think that making this slightly easier to do will result in it being more widespread. What reason does malware have to do this that isn't better served by DNS Hijacking + installing a root cert?

nitrogen• 11 years ago

I have seen malware that repeatedly adds a compromised root certificate to a machine's trusted authorities.

Torgo• 11 years ago

I just dealt with this a couple months ago, and had to explain to my boss why I reverted from best-practice SSL settings in the course of trying to solve a tricky problem. Another issue I ran into was, the current packaged version of Wireshark in Ubuntu had some bugs in it that also prevented me from decrypting traffic (it didn't tell me this, it just didn't work and I had to track down the problem myself.) I had to compile the latest from their website to finally get everything working.

ecesena3• 11 years ago

Very interesting combo!

Another technique that often, sadly, works is the old school man-in-the-middle.

I was recently looking at the api of an app on my phone, using ettercap to arp poison my phone and capture traffic on my laptop. Found the api call was over https (fwd secrecy and all looking good), I tried ssl-mitm with a fake cert... no errors in the app, clear text on my laptop. Happy and sad at the same time. :/

mdaniel• 11 years ago

What an amazing and scary tool (maybe those always go together). I now have a much deeper appreciation for why folks are afraid of Starbucks WiFi.

notfoss• 11 years ago

Any decent browser will display a certificate error for a Mitm attack. But yes, if you are using other programs/apps over an untrusted network, you can never be sure.

ecesena3• 11 years ago

It's not actually about the WiFi, secure or not. I was in a WPA2 WiFi. I attacked my phone (at a higher network level), so unless there's an active IDS in place, you can't do much about it.

The issue is not the network, but the way the app continued over an insecure connection.

mobiplayer2• 11 years ago

Wait a second...

Was the fake cert trusted by your phone? If affirmative, did you manually add the root cert from your fake CA or at least accepted that cert as trusted?

If you didn't explicitly trust that cert and the application didn't complain we're in front of another completely wrong use of SSL.

ecesena3• 11 years ago

No, not trusted. That's why I was sad. The app failed to verify the certificate chain and silently continued over the (in)secure connection.

nailer• 11 years ago

Small super-pedantic note: the correct file 'so that it is set every time you log in' on both OS X and Linux would be .bash_profile.

- .bashrc is run every time the shell is started (eg, subshells, su without -l or -)

- .bash_profile is run only when a 'log in' shell is started, eg, a tty, su -l, su-, new tab, etc.

Animats3• 11 years ago

That article seems to be a rewrite of this 2012 article: http://www.root9.net/2012/11/ssl-decryption-with-wireshark-p...

A SSLKEYLOGFILE environment variable makes Firefox and Google Chrome silently log their crypto keys as plaintext. What could possibly go wrong?

This 2014 discussion (https://groups.google.com/forum/#!topic/mozilla.dev.tech.cry...) says that originally the documentation for this feature said that it was only turned on in debug builds of Firefox. Then, somehow, it was quietly turned on for all builds, with no notification.

Take a look at the code in Firefox for this:

https://hg.mozilla.org/projects/nss/file/65605e800fd1/lib/ss...

Firefox understands several suspicious environment variables: SSLBYPASS, SSLKEYLOGFILE, NSS_SSL_REQUIRE_SAFE_NEGOTIATION, NSS_SSL_ENABLE_RENEGOTIATION, and NSS_SSL_CBC_RANDOM_IV, all of which have security implications. Some were put in for some Thunderbird problem involving Microsoft mail servers, but the common library may enable them in Firefox as well. That whole section of code should be present only debug builds, if at all.

It's funny how backdoors like this keep creeping into mainstream software, isn't it. Look at the code histories and see who put in those changes.

scintill76• 11 years ago

This does seem, at the least, irresponsible of the browser vendors. I'll be especially angry if Chrome doesn't have very prominent warnings, considering they harass some developers and power users with a warning about an "insecure" configuration Google basically forced them to use.[0] By analogy, I expect nothing less than a blinking red warning covering the entire browser window whenever keys are being logged because of an environment variable.

I also don't think readers should be encouraged so readily to put this into the persistent global environment.

[0] https://code.google.com/p/chromium/issues/detail?id=337734

reubenmorais• 11 years ago

Chrome uses NSS, so the GP applies exactly to it: https://code.google.com/p/chromium/codesearch#chromium/src/n...

nodata3• 11 years ago

Why are you calling this a backdoor?

weland• 11 years ago

It could be named "A rather unfortunate architectural decision that can make browsers write keys in plaintext without users explicitly enabling it" but that would be a little verbose. A malicious program can add a SSLKEYLOGFILE environment variable (if it's not systemwide, it doesn't need root privileges for that).

I guess we can haggle over whether or not this meets the "definition" of a backdoor. "Can give unrestricted access to encryption keys" is backdoor in my book, but I'm not a fan of taxonomy, the retarded child of sciences :).

I can understand why this... um, this feature, would be useful in developer builds. Why it's present in anything that is shipped to users is beyond my ability to comprehend. It should be behind an ENABLE_DANGEROUS_PLAINTEXT_LOGGING switch that is off by default. What's the thought process by which someone decides giving this to users is a good idea? Is there something I'm missing here?

Animats3• 11 years ago

Some of those environment-variable "features" were workaround for problems in the past. Many of those could probably be removed outright. All of them should be removed from non-debug builds.

Legogris• 11 years ago

If you're going to debug your own services (where you can own the certificate key) you can also do this easily by tcpdump and then importing the encrypted dump and decrypting it inside Wireshark: http://support.citrix.com/article/CTX116557

I had to verify how two services (not web browsers) were communicating the other day and this was the easiest solution for me.

andor• 11 years ago

Take a look at the first paragraph. With Forward Security, having the private key is not enough, you need the session keys.

Decrypting TLS Browser Traffic with Wireshark

Related Stories