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I personally trust Google in terms of security but I'm not sure whether man-in-the-middle (MITM) attacks against Google services AS OF TODAY possible or not. As far as I know, Google uses some protections against (MITM) regarding certificates in Chrome browser. Is MITM possible for Google services (TLS/SSL) as of today?

user215422
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  • The word "today" makes your question off-topic, as "today" means the answers will likely change in the future. – ThoriumBR Nov 26 '19 at 22:06
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    @ThoriumBR I think Security is always a point of view. 1994 SSL 1.0 was the best technique. Today we know that it wasn't that good. Now we are at TLS 1.3 . – Cyberduck Nov 26 '19 at 22:47
  • @ThoriumBR It can still be detected that the question was asked 2019 and that it reflects the views of the time. –  Nov 28 '19 at 12:11

2 Answers2

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MITM is still possible if the attacker has sufficient control over the endpoint or in some cases if there is already SSL interception going on (not uncommon just by using AV).

If the attacker is able to either install a new CA on the endpoint or can use an existing custom CA already installed on the endpoint (as in case of the Superfish CA which was installed on Lenovo Systems) then he can do MITM. No HSTS or certificate pinning or certificate transparency will help in this case since these are deliberately disabled when a custom CA is used.

Similar MITM could be done in some cases if SSL interception is already in place. This is for example the case with many desktop AV software (Kaspersky, ESET, Avira ... all can do it and will often do it by default) and it is also common in companies. The necessary CA certificates for interception are automatically put into the trust stores and the client never sees the original certificate but must trust the SSL interception device/software to do a proper job. Unfortunately SSL interception systems commonly don't check for certificate pinning and certificate transparency in the first place, which makes it possible to use a different and compromised CA for the Google certificates then usually used. Moreover some SSL interception systems are of such a shoddy quality or configuration that they don't properly check certificates at all and can thus be fooled with certificates created by an attacker.

And of course SSL interception could be done if the attacker is able to compromise the device or software which does the SSL interception. Unfortunately systems like firewalls are not as hardened as one might hope and it is not uncommon that bugs surface which allow an attacker sufficient control over such devices.

Steffen Ullrich
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  • Thanks for detailed and informative answer. If there is a preinstalled root certificate that is provided by an actually untrusted CA in Android device, does certificate transparency or other technic used by Google work for MITM against Google services? (Assume that Android device is used, no AV or firewall for SSL interception, no company network, only normal user) – user215422 Nov 27 '19 at 11:53
  • @user215422: If there is an explicit root CA installed then it can be used for MITM and this includes access to Google. This is at least true for the browser, it might be that applications are more restrictive in this regard. – Steffen Ullrich Nov 27 '19 at 14:09
  • Is the only solution deleting/disabling a preinstalled but untrusted CA's root certificate? (for a regular user who uses home internet). – user215422 Nov 27 '19 at 19:50
  • @user215422: I'm not sure if this is what you mean but as far as I know there is no way to enforce certificate pinning if a custom CA is trusted and the certificate was issued by it. – Steffen Ullrich Nov 27 '19 at 20:35
  • If an ISP make MITM against Google services, can Google understand and protect us as of today? – user215422 Nov 27 '19 at 20:53
  • @user215422: While MITM can be detected on the server side with heuristics (SSL client fingerprinting like JA3) I doubt that they will be able fully distinguish legal SSL interception from an attack, which means that they likely don't do anything just based on MITM alone. They might try to detect strange behavior though by using a combination of features and detected MITM might be one of these. But this is just speculation on what is likely possible - I don't know what they really do. – Steffen Ullrich Nov 27 '19 at 21:01
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Generally Google and its services are using TLS connections on all sites. With the usage of this it won't be possible for attacker to intercept your traffic. There are also various techniques which mitigate attacks on this connections.

I would suggest to look for:

These three techniques ensures that no man in the middle will be possible.

Cyberduck
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  • If an employee connected via their company network is using one of Google's services via SSL/TLS, and the company is executing a 'corporate MITM' attack using a root certificate that the company installed in the employee's web browser (a la Steve Sether's answer at https://security.stackexchange.com/questions/101721/is-it-possible-for-corporation-to-intercept-and-decrypt-ssl-tls-traffic), then would the employee's web browser show any warnings or errors? – mti2935 Nov 26 '19 at 22:26
  • Do Public Key Pinning or any other protection used by Google works if any trusted root certificate on device used for MITM? – user215422 Nov 26 '19 at 22:31
  • @mti2935 No. This would be ssl interception and is normal behavior inside companies. This can only be detected by manually looking onto the certificate. (A warning will occur if you surfed once on a google site.) – Cyberduck Nov 26 '19 at 22:31
  • @user215422 If I understand your question the right way I would say yes. Public key pinning still works if you use ssl interception you just don't notice this if you do not look on the certificate. Take a look on this question: https://security.stackexchange.com/questions/129266/is-ssl-interception-possible-without-disabling-public-key-pinning-on-the-client – Cyberduck Nov 26 '19 at 22:38
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    @CDRohling Thanks. The article about Public Key Pinning says "The mechanism was deprecated by the Google Chrome team in late 2017 because of its complexity and dangerous side-effects.". As I understand, it's not available now in Chrome. – user215422 Nov 26 '19 at 22:50
  • @user215422 Yea sorry forgot about that. Now they use Certificate Transparency. I updated my answer – Cyberduck Nov 26 '19 at 22:51
  • @CDRohling As I understand, we can say that "MITM is not possible as of today for Google services". Am I right? – user215422 Nov 26 '19 at 23:00
  • @user215422 possible is a hard word. I am thinking that everything is possible on the internet. It is just very very hard and noone has achieved it till today (We don't know anyone) – Cyberduck Nov 26 '19 at 23:05