[tor-bugs] #24351 [Applications/Tor Browser]: Block Global Active Adversary Cloudflare

Tor Bug Tracker & Wiki blackhole at torproject.org
Mon Nov 20 21:55:53 UTC 2017

#24351: Block Global Active Adversary Cloudflare
 Reporter:  nullius                              |          Owner:  tbb-
                                                 |  team
     Type:  enhancement                          |         Status:
                                                 |  reopened
 Priority:  High                                 |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  security, privacy, anonymity, mitm,  |  Actual Points:
  cloudflare                                     |
Parent ID:  #18361                               |         Points:
 Reviewer:                                       |        Sponsor:
Changes (by nullius):

 * status:  closed => reopened
 * resolution:  invalid =>


 Replying to [comment:7 cypherpunks]:
 > You can't tell unless you have access to a site owner's Cloudflare
 account whether they have full SSL with Cloudflare or whether Cloudflare
 is MiTMing them, so this doesn't seem possible.

 Either you are obfuscating, or you are technologically incompetent.  Quick
 proof:  Assume the opposite.  If Cloudflare did not act as a MITM proxy
 with full, active access sufficient to read ''and modify'' TLS plaintext
 of all connections passing through them, then they would be unable to
 inject the HTTP headers which this bug proposes to detect for blocking.
 [Sequential dotted initials “Q.”, “E.”, “D.” forbidden by Trac spam

 Cloudflare is a MITM, ''by design''.  That is the primary (only?) service
 they offer.  It does not matter what the site’s service level with them
 is.  From the connecting user-agent’s perspective (here apropos), it does
 not even matter if the site uses its
 /keyless-ssl-the-nitty-gritty-technical-details/ so-called “keyless SSL”]
 service to preserve secrecy of its ''long-term'' private keys.  Cloudflare
 always, always has the symmetric key to the session; and within the
 ostensibly encrypted session, Cloudflare is by definition a Man-In-The-
 Middle which decrypts, modifies, and proxies the plaintext.

 Why, it is exactly as if Cloudflare were designed as a mass surveillance
 tool!  So, what rationalizations could be supposed for those who use their
 services, or ignore them as a global threat?

 “But Cloudflare is a trustworthy provider of Internet infrastructure.”
 Then, why do we need TLS at all?  Just make peering arrangements with
 trustworthy networks who agree to pass your packets only through
 trustworthy routers!  TLS eliminates trust in the network:  By design, TLS
 promises end-''to-end'' encryption.  Meaning, with the ''endpoint''.  By
 design, Cloudflare makes a mockery of this promise.

 “But most sites are on third-party hardware, anyway.”  Irrelevant:
 Cloudflare centralizes trust.

 Without the Cloudflare MITM proxy, `little-newbie-web-shop.com`’s TLS is
 handled by `cheap-shared-web-host.com`; `chic-trendy-cloud-buzzword-
 startup.com`’s TLS is handled by AWS; `at-risk-controversial-activism.org`
 and `high-security-bitcoin-services.com` should (we hope) do all their
 crypto on hardware under their respective owners’ physical control.  The
 site visitor is responsible for deciding which endpoints to trust with
 private information.  (N.b.:  Reading interests and “clicktrails” are
 private information.)  When all these sites sign up for Cloudflare, then
 Cloudflare becomes the one-stop decryption shop.  Do you trust Cloudflare
 to ''be'' the “secure” Internet, or some huge proportion thereof?

 Centralizing trust has a much worse effect than allowing access to many
 individual sites:  It creates a single point at which to perform mass
 dragnet surveillance.  As of today, Cloudflare has access to the plaintext
 data of more TLS sessions to more endpoints than anybody else on
 Earth.![1]  Here, the whole is more than the sum of the parts:  They are
 in a position to track, tap, ''and link'' Internet activity across a wide
 range of sites.  This is why they have been declared a [ticket:18361
 Global Active Adversary].

 If I were the NSA or another TLA, and I sat down to design a mass-
 interception network to MITM TLS on a large portion of the Internet, then
 the result would look exactly like Cloudflare.  They are in a position
 where they in fact do intercept the communications of billions of people
 with millions of websites.  That is not a hypothetical:  It is a
 description of what they actually do—every day, ''right now''.  Then, they
 cross their fingers and promise to respect people’s privacy.  “Trust us;
 we will make you ‘safer’.”  Again—why use any encryption at all?

 On that level, Cloudflare is even worse than “key escrow” or another
 backdoor would be.  Since the 90s, advocates of “key escrow” have promised
 that if centrally trusted parties are allowed to keep a backdoor key, then
 that would really, truly only ever be used to intercept the communications
 of whatever they deem “bad guys”.  (Pinky swear!)  Cloudflare walks in
 through the front door, and takes the plaintext—all of it, without
 exception, for everybody whose connections pass through them.

 And worst of all, the design of Cloudflare removes responsibility and
 decision-making power from the initiator of communications.  End-users are
 fooled into believing they connect to many different sites—all of which
 run through a single chokepoint.  '''The purpose of this bug is to
 mitigate that problem, in a web browser specifically designed for
 security, privacy, and unlinkability on an anonymity network.'''

 “But we need Cloudflare to protect from DDoS.”  Hey, that’s a nice site
 you have there.  It would be a shame, such a shame, if anything happened
 to it.  Why don’t you let us decrypt all your TLS sessions, so we can
 protect you?

 Cloudflare only exists because of criminal activity which can be otherwise
 defended against, and which should not be possible at all.  They profit
 from fear of vigilante network censors, hold-your-site-hostage
 blackmailers, and Internet arsonists who simply enjoy setting things on
 fire for the “lulz”.  The proper long-term solution to these problems
 involves serious technical work to make DDoS attacks more difficult to
 perform (and especially, harder to amplify).  The proper short-term
 solution involves sysadmins working with competent hosts and upstream
 providers—just as is done by many sites which are not Cloudflare
 ~~patsies~~ customers.  (I notice that torproject dot org, a controversial
 website, somehow manages to survive without Cloudflare.)  Routing the TLS
 plaintext of millions of websites through a single MITM is ''not'' a

 Anyway, the reason why sites use Cloudflare is irrelevant.  This bug is
 about user choice, informed decisions, and frankly, the honesty of the
 network.  When I see the lock icon in Tor Browser, I take that as a
 guarantee that my connection is end-to-end encrypted.  '''If a site uses
 Cloudflare, then the browser lock icon is a false promise.'''  When I use
 Tor Browser to make a https connection, I also quite reasonably expect
 that it will terminate the connection with an error message if it detects
 any evidence whatsoever a MITM attack.  In this sense, blocking or warning
 on detection of `CF-RAY:` is more reliable than, say, disallowing self-
 signed certificates:  The latter could be the genuine certificate of a
 website configured by a doofus, or it could be a `BadExit` running
 `sslstrip`, or it could be network naughtiness by hackers (on the
 government payroll or otherwise).  `CF-RAY:` is ''always'' the result of a
 definitional MITM attack by a Global Active Adversary.

 In sum, “[ticket:24321 CAPTCHA madness]” is the smallest problem with
 Cloudflare.  Their design, their business model, their very existence is a
 threat to the privacy, security, and freedom of the Internet.  Blocking
 Cloudflare is an eminently reasonable mitigation strategy for a web
 browser which bears the name, “Tor Browser”.  Bug re-opened.

 1. Source:  I just assume as much; but Cloudflare would brag about that,
 if restated in other words as on their homepage:
 Cloudflare makes more than 6,000,000 Internet properties faster and
 safer.]”  Yes, they provide “secure CDN” service to more sites than
 anybody else.  Do you know of anybody else who actively MITMs that many
 TLS endpoints?

Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24351#comment:8>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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