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brave / brave-browser

Brave browser for Android, iOS, Linux, macOS, Windows.
https://brave.com
Mozilla Public License 2.0
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tor leak over OCSP for EV certs? #14262

Open diracdeltas opened 3 years ago

diracdeltas commented 3 years ago

STR:

  1. open new tor window with wireshark running and filter wireshark by ocsp
  2. go to https://brave5t5rjjg3s6k.onion/new-onion-service/
  3. you see an OCSP request that contains the onion service's serial number: 0A 7A 97 E8 F3 EE C2 BD 60 A6 FD 5E 82 36 35 0C
Screen Shot 2021-02-19 at 10 36 35 AM

you can also repro this for non-onion website like https://gdpr.org (04 28 EA A2 19 7C 7B 01 17 AB 7E 86 B1 2B 9F E7 51 99):

Screen Shot 2021-02-19 at 10 55 58 AM

note that you may not see results for system-cached OCSP responses if you've already visited the site.

diracdeltas commented 3 years ago

pretty sure this is because Chromium delegates stuff to the system TLS stack (which doesn't respect chromium proxy settings) on macos/win

fmarier commented 3 years ago

Interesting, I was under the impression that OCSP was disabled in Chromium:

Online (i.e. OCSP and CRL) checks are not, generally, performed by Chrome. They can be enabled by policy and, in some cases, the underlying system certificate library always performs these checks no matter what Chromium does.

https://dev.chromium.org/Home/chromium-security/crlsets

diracdeltas commented 3 years ago

@fmarier i think the key sentence is in some cases, the underlying system certificate library always performs these checks no matter what Chromium does.

there may not be a straightforward way from chromium to tell the underlying system library not to do OCSP checks for particular URLs or processes

darkdh commented 3 years ago

I think this also applies to non-EV certs when system ocsp cache doesn't have that entry. For EV certs, when it is also not found in CRL set, chromium will do an extra OCSP lookup which doesn't allow soft-fail unlike the first lookup. Also disabling OCSP and only check CRLs is not sufficient because CAs aren't required to publish CRLs, many don't.

We can wait for CertVerifierBuiltin to be stable on Mac and upstream will look at Windows support https://chromium-review.googlesource.com/c/chromium/src/+/2171996/4/net/features.gni Linux is using it by default https://chromium-review.googlesource.com/c/chromium/src/+/2171996/4/net/cert/cert_verifier.cc