[tbb-bugs] #25929 [Applications/Tor Browser]: Critical breach in first-party isolation allowing users deanonimization and profiling

[Tor Bug Tracker & Wiki]

#25929: Critical breach in first-party isolation allowing users deanonimization and
profiling
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     Reporter:  cypherpunks               |      Owner:  tbb-team
         Type:  defect                    |     Status:  new
     Priority:  Immediate                 |  Milestone:
    Component:  Applications/Tor Browser  |    Version:
     Severity:  Critical                  |   Keywords:
Actual Points:                            |  Parent ID:
       Points:                            |   Reviewer:
      Sponsor:                            |
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 1 An adversary crawls the web creating a database storing the info about
 which website uses which certificates in the chain of trust, including
 resources.
 2 The adversary setups a malicious website evil.com having large amount of
 subdomains each one using different certificates in the chain of trust,
 but NOT SENDING ALL OF THEM, each domain skips sending a single
 intermediate certificate.
 1 A user opens a website stupid.com
 2 The website stupid.com uses different resources from different sites
 using different CAs. All the certs are cached.
 3 User closes stupid.com and visits evil.com. The website includes single
 pixel transparent images (or other resources) from all its crafted
 subdomains.  If an intermediate cert is cached the connection succeeds. If
 it isn't it fails. This way the adversary knows which intermediate certs
 are cached and can reduce its uncertainty about the websites visited by a
 user. the attack doesn't require any JavaScript or CSS, only images.
 4 If an adversary controls some of resources of stupid.com it can craft an
 unique set of intermediate certificates for every its user.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25929>
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